i
FROM QUANTUM CORPORATION
Quantum
®
DLTtape™Handbook
Your Complete Guide to Today’s
Hottest Storage Technology
Eighth Edition
Notice
Editor
Peter McGowan
g•m marketing
communications
Associate Editor
Stephen Weekley
Quantum Corporation
Senior Wr iter
Hank Giles
g•m marketing
communications
Art Director
Christine Koch
Knockout Graphics
Illustrator
Steve Hussey
Copyright ©1997, 1998, 2000,2001 Quantum Corporation
QUANTUM CORPORATION
501 Sycamore Drive
Milpitas, CA 95035
1-800-624-5545
www.quantum.com orwww.DLTtape.com
Quantum and the Quantum logo are trademarks of Quantum Corporation, registered in the U.S.A.
and other countries. DLTtape, the DLTtape logo,Super DLTtape, and the Super DLTtape logo are
trademarks of Quantum Corporation. Products mentioned herein are for identification purposes
only and may be trademarks or registered trademarks of their respective companies.Quantum is not
responsible for typographical, editorial, or pictorial errors in this publication.Product specifications
and technical information are subject to change without notice.
ii
Foreword
The world of data storage has changed a great deal since we published the first Quantum DLTtape
™
Handbook in 1997.In just this
short time, the role of storage has evolved dramatically.It has
become clear that effective storage strategies are fundamental to
the success of virtually any information technology strateg y,
whether it’s in re-energized smokestack industries or e-commerce.
Since the first Quantum DLTtape Handbook,we now have published a total of eight editions, plus two editions in Japanese and
one in Chinese.And, while the roles of storage and DLTtape technology have changed and evolved with incredible speed, the
objective of the handbook is stil l much the same as it was originally: to educate our various audiences by providing an in-depth look
at DLTtape system technology and a comprehensive overview of
DLTtape products and solutions. The book will also g ive you a
context for understanding how storage technology has evolved into
such an integral part of enterprise IT str ategy, and the role
DLTtape technology plays.
The most notable change in the content of this eig hth edition is
the inclusion of extensive information on the new Super DLTtape
™
technology,the next generation of DLTtape technology.Super
DLTtape technology delivers dramatic increases in DLTtape speed
and capacity,while continuing the DLTtape commitment to compatibility with previous generations of drives and media.
Incorporating a number of important technology innovations,
Super DLTtape technology promises to broaden the role of the
QUANTUM DLTtape HANDBOOK
iii
DLTtape system as the dominant tape technology for backup,
recovery, archiving, vaulting, near on-line storage, and multimedia storage hierarchies.
Because Super DLTtape technology is the newest development in
DLTtape systems, we have included in this edition of the handbook
a great deal of new information specific to Super DLTtape technology.However,it is important to emphasize that, while Super DLTtape
technology includes a number of breakthrough innovations,it is
not a “new”technology : it is an extension of all the concepts that
have made the DLTtape systems so successful since the original
linear tape technology was introduced in 1985.So when we use the
term “DLTtape systems”or “DLTtape technology”throughout this
book, we refer to all DLTtape technology,including Super DLTtape
technology,and the entire DLTtape family of products,including
the newest Super DLTtape drives and media.
Welcome to the eighth edition of the Quantum DLTtape
Handbook,and to the exciting possibilities of a whole new
generation of Super DLTtape systems.
FOREWORD
iv
Contents
Chapter
— Introduction
— 1. The Evolving Tape Storage Market
— 2.What is the DLTtape System?
— 3. History of DLTtap e Technology
— 4.Why Customers Want the DLTtape System
— 5. Reliability: The Heart of the DLTtape System
— 6. Demystifying Tape Drive Specs
— 7. DLTtape Media
— 8.Automation
— 9. Horizontal Applications
— 10.Vertical Market Applications
— 11. DLTtape System Technology Compared
— 12. Evaluating the Cost of a DLTtape Backup Solution
— 13. Platform Connectivity & Software Compatibility
— 14. Storage Management Software
— 15. Firmware
— 16. Using the DLTtape System
— 17. Super DLTtape: The Future of DLTtape Technology
— Appendix A: Super DLTtape System Products
and DLTtape System Products
— Glossary
— Index
Page
vii
1.1
2.1
3.1
4.1
5.1
6.1
7.1
8.1
9.1
10.1
11.1
12.1
13.1
14.1
15.1
16.1
17.1
A.1
G.1
I.1
QUANTUM DLTtape HANDBOOK v
vi
Introduction
This handbook will introduce you to one of the dominant forces in
mid-range storage technology – the DLTtape systems, including the
new Super DLTtape systems.These systems are the acknowledged
market-share leaders in mid-range tape backup and archiving, thanks
to their remarkable performance,reliabilit y,and storage capacity.
Convergence Emergence
Why has a seemingly mundane topic like backup and archiving
become such a hot subject in recent years? There are several
answers.A number of trends are converg ing to create a new and
seemingly limitless hunger for faster, higher capacity storage backup systems. These trends include:
•
The growth of Internet, Intranet, and e-commerce
applications, many of which require constant backup of ver y
large databases.
•
The popularity of storage-intensive applications like multi-
media, data warehousing, v ideo editing, medical imaging,
financial analysis, and engineering .
•
Centralized backup management of distributed,
networked systems.
•
Exponential increases in hard disk capacity and performance.
QUANTUM DLTtape HANDBOOK
vii
•
A shrinking “window”for backup and archiving.
•
The emergence of enterprise level storage management
strategies, including Storage Area Networks.
In this handbook,we will show you why DLTtape and Super DLTtape
drives and media are the best storage solutions for these and many of
the other storage challenges you may face.We will also help you evaluate your DLTtape storage options and pick the solution that’s right
for you.
We’ve Got You Covered
To help you understand DLTtape technology and how it fits into
your IS backup picture,we’ve included chapters that cover everything from the history of DLTtape drives and media to a detailed
comparison of competitive backup solutions.Here’s a sample of
what we’ll cover:
•
What is the DLTtape system?
• What is Super DLTtape technology?
•
Why customers want DLTtape drives and media – the
DLTtape system.
•
Applications for the DLTtape system.
•
What makes the DLTtape system so reliable?
•
Why the DLTtape system is perfect for autoloaders,librar ies,
and Storage Area Networks (SANs).
•
What makes DLTtape cartridges special.
•
Platform connectivity considerations.
•
The br i g h t f ut ure o f Super DLTtape technology.
Welcome to the new world of storage management.Welcome to
the world of the DLTtape and Super DLTtape systems from
Quantum Corporation.
INTRODUCTION
viii
The Evolving
Tape Storage Market
QUANTUM DLTtape HANDBOOK
1
1.1
Before we plunge into the story of the DLTtape system, we need
some context. Who’s buying DLTtape drives and media? And,more
importantly,WHY? In this chapter, we’ll walk you through some of
the market forces that are impacting the industry, including:
•
Trends in computing systems: moving away from centralized
computing, toward a client/server model.
•
Moving to centralized management of dist ributed systems.
•
Growth of mission critical, leading edge applications.
•
Dramatic advances in tape technology for backup.
Market Si ze
The market for tape drives is projected at $6 billion a year for the
next few years,with unit shipments holding steady at about 4 million per year, worldwide. Almost all of those 4 million units are going
to be used for backup.
But,while unit shipments will remain steady, the amount of data that
needs to be backed up is growing rapidly. For example, it is estimated
that in 1999 worldwide server capacity,one important category of data
that needs to be backed up,was less than 500 petabytes (Figure 1.1). By
2004,that figure will have multiplied to over 4,300 petabytes!
THE EVOLVING TAPE STORAGE MARKET1.2
With the projected amount ofdata that needs to be backed up climbing at a rapid rate,and the projected growth in tape drive units shipped
staying relatively flat,each of those backup tape drive units must deliver more capacity than ever before.Analysts project that there may be
the potential for a melt-down if the backup technology does not keep
up with that sharply rising demand curve.The continual evolution of
DLTtape technology and the dramatic increase in capacity and performance delivered by Super DLTtape technology are a direct response to
this need.What factors are driving this rising demand for backup
capacity? Let’s start with computer systems trends.
From Mainframe to Client/Server
The deployment of client/server systems is accelerating.From 1994
to 1996,the percentage of organizations that said they were actually
using client/server systems grew from 25 to 44 percent.Today,
client/server is the dominant mainstream approach to enterprise
0
500
1,500
1,000
2,000
2,500
3,000
3,500
4,000
4,500
1999 2000 2001 2002 2003 2004
Centralized
Network
Centralized
Administration
Distributed
Workgroups
SOHO
Networks
Worldwide Server Capacity (in Petabytes)
Source: Strategic Research Corp., Network Demographics, 2000
Figure 1-1 Worldwide Server Capacity is one measure of data to be
backed up. The figure is climbing at a much steeper rate than the rate of
tape shipments. Backup capacity must increase to match increased storage
demands in this and other categories.
QUANTUM DLTtape HANDBOOK 1.3
computing.For storage and backup,this means a shift away from the
high-end products used in mainframe environments (reel-to-reel
tape),and away from low-end,PC-oriented products (4mm DAT),
and toward the mid-range (8mm and half-inch DLTtape systems).
New Storage Strategies
New storage strategies are also driving the market for DLTtape technology.Two good examples are Storage Area Networks and Network
Attached Storage.A Storage Area Network (SAN) is a high-speed,
special-purpose local network that provides a large pool of storage
resources and makes it easily available to the enterprise network.
SANs are usually deployed to support applications that require large
amounts of storage, and to support large, enterprise-le vel networks.
Most SANs depend on large DLTtape-based libraries to back up disk
storage. SAN revenues are expected to grow from under $4 bil lion in
1999 to over $20 billion in 2004,according to IDC.(See Figure 1-2.)
Another indicator of the size of this market opportunity for DLTtape
0
20
16
12
8
4
1999 2000 2001 2002 2003 2004
Source: IDC December 2000
SAN
NAS
Worldwide SAN and NAS Revenues in $ Billions
Figure 1-2 SAN and NAS Disk Shipment Revenues will continue to grow
quickly as these storage concepts are implemented widely.
0
1997 1998
3,000
2,000
2,500
1,000
1,500
500
1999 2000 2001 2002 2003
Worldwide F ibre Channel Hub and Switch Rev enue ($M)
Source: IDC April 2000
Figure 1-3 Worldwide Fibre Channel Hub and Switch Revenues.
Storage Area Networks (SANs) incorporating Fibre Channel technology will
grow as the preferred enterprise storage strategy, as evidenced by the projected growth in Fibre Channel network hardware revenues. DLTtape technology
plays an important role in the consolidation of backup to these large storage
networks.
technology is the rapid growth in Fibre Channel hub and switch revenues.(See Figure 1-3.)
Network Attached Storage (NAS) is simply storage that is deployed
independently on a Local Area Network.NAS products feature a pluggable Ethernet connection for easy installation.Target market applications include file server,desktop,remote office installations,software
distribution, and emerging applications such as audio,video,and
Internet storage.DLTtape is a perfect complement to the growing
storage needs NAS solves.A user can easily grow their storage requirements and still back up the network through a DLTtape solution. IDC
projects that NAS revenues will grow from under $1 billion in 1999 to
nearly $15 billion in 2004.(See Figure 1-2.)
THE EVOLVING TAPE STORAGE MARKET1.4
Centralized Management
The management of information resources has been evolving from
the totally centralized “glass house”systems of the 1970s and 1980s
(see Figure 1-4).In the late 1980s and into the 1990s,the client/
server model emerged. Computers were distributed, storage was
distributed, and the management of distr ibuted resources was itself
distributed. To some extent, the mainframe-or iented management
structure was weakened.
However, without centralized, professional management,decentralized
computing systems are in danger of reducing system reliability,data
integrity,and security.Now, at the beginning of the 21st century,the
trend is for information resources to contin ue to be distributed,but for
resource management – including storage management – to become
more centralized,under a professional management team, using highlevel,highly integrated management tools,and more and more
automation.
Centralized management of storage resources has a powerful impact
on backup systems,creating a demand for universal backup strate-
QUANTUM DLTtape HANDBOOK 1.5
Figure 1-4 The Storage Management Evolution shows a transition to re-
centralized storage management and a continuation of distributed data resources.
Time
Regime
Early 1980s
Late 80s–90s
Late 90s
Early 2000s
Glass House
Client/Server
Professionally
Managed
Automated
Central
Distributed
Central
Central and
Distributed
Central
Distributed
Distributed
Central and
Distributed
System
Management
Location
of Data
Location of
Data Management
gies. There is a greater demand for standard solutions, and robust,
highly reliable systems for mission critical applications. Large, g lobal
enterprises demand global backup and disaster recovery plans.
The system-level trends we’ve been talking about – the move to
client/server,the emergence of Storage Area Networks, and the
strong trend toward centralized management of distributed storage
resources – are increasing the demand for bigger,smarter tape
backup systems.And that’s where the DLTtape system fits.
Now let’s look at another set of trends that are having a major
impact on tape backup issues. Namely, trends in applications.
Mission Critical Applications
Yesterday’s mission-critical applications were back office tasks like
payroll,accounts receivable,and accounts payable.They were mission
critical because the business needed them to function.Today’s mission critical applications must run 7x24, and they are often very customer-oriented,highly visible, and strategic. E-commerce applications like on-line banking,ticketless airline reservations,or on-line
stock transactions are prime examples.Almost by definition, these
customer-interfacing applications are client/server applications, so
they have to run outside the protection of the old “glass-house”
mainframe environment.
This means that there is intense pressure to keep these applications
aggressively backed up, and within a shrinking window of time. If
the application is up on a 7x24 schedule, when can you do backups? Solutions to this problem include more frequent backups,
more servers with their own dedicated backup systems, and bigger,
faster systems to fit backup into the shrinking backup window.
Clearly, the introduction of new high perfor mance, hig h capacity
Super DLTtape systems has a major impact on backup capability.
THE EVOLVING TAPE STORAGE MARKET1.6
Vertical Markets
Growth in specific vertical markets is pushing the demand for better
backup solutions. Internet/Intranet applications are growing at a
very fast rate. They are driving the sales of servers,and they are also
driving the sale of a large amount of storage capacity.An increase in
storage capacity always drives the need for more backup capacity.
Internet and Intranet applications, impose heavy backup demands
for several reasons.They run around the clock, so the backup window is always under pressure, they change constantly,they tend to
grow in size,and their content is increasingly graphical and therefore
storage intensive.Ver tical markets driving the demand for DLTtape
backup include:
• E-commerce.
• Internet/Intranet.
• Archiving.
• Disaster recovery.
• Data mining .
• Medical imaging.
• Graphic ar ts.
• CAE/CAD/CAM.
• Multimedia.
• Publishing.
• Data acquisition.
•Video-on-demand.
• Dig ital nonlinear video editing .
•Video distribution.
• Storage Ser v ice Providers (SSPs).
• Application Service Providers (ASPs).
In Chapter 10,we will go into more detail on the special backup
needs of various vertical applications.
QUANTUM DLTtape HANDBOOK 1.7
Content is Everything
Another trend driving the DLTtape system market is the shift in
application content.When images, color,full motion video,and
audio are added to the content mix,storage requirements explode.
This growth is generating demand for high capacity storage, and
for backup.
Applications that use non-traditional content have other requirements beyond just size.For instance,these applications often
involve distribution of content (for example, programming for
video-on-demand applications). It is important to have durable,
reliable media that can stand up to the abuse of shipping, frequent
use, and storage in hostile environments.
Tape Technolog y Trends
Trends at the system level and in applications are driving changes
in the tape backup market.Another factor in the evolving tape
market is the changing tape technology itself.
One of the most important trends in the tape environment is the continuing proliferation of incompatible tape formats. New tape formats
are being introduced,not by newcomers and start ups, but by some of
the biggest names in the technology world.A review of available tape
technologies would include 4mm DAT,8mm,quarter-inch (QIC),and
half-inch,including the DLTtape system.There have always been
options available,and new options keep coming. There are quarter
inch cartridge (QIC) drives that use quarter-inch tape,and there is
quarter-inch tape that is actually .315 inches wide.There are three different types of 4mm DAT tape: DDS-2, DDS-3, and DDS-4.
Fortunately, the latest and the highest capacity DDS-4 tapes are backward compatible with the earlier versions.That isn’t always true as
THE EVOLVING TAPE STORAGE MARKET1.8
new technologies come out.For example, Sony’s 8mm tape (AIT) and
Ecrix’s VXA are not compatible with other 8mm tapes on the market.
It appears that there are more formats available than the market
can possibly use. To a certain extent, the formats sor t themselves
out naturally.QIC and 4mm products are designed for low end
applications, primarily for PC and small network backup, while
8mm and DLTtape system half-inch products are flourishing in the
mid- and high-end ranges.
Figure 1-5 DLTtape System Product Family includes the DLT 4000 drive,
the DLT 8000 drive, the DLT1 drive and the SDLT 220 drive, as well as the DLTtape III,
DLTtape IIIXT, DLTtape IV, and Super DLTtape I cartridges. DLTtape drives are available in desktop and system-installable units.
QUANTUM DLTtape HANDBOOK 1.9
DLT 4000
drive
DLT 8000
drive
SDLT 220
drive
DLT1
drive
DLTtape IV
DLTtape III
DLTtape IIIXT
Super DLTtape I
Capacity
(GB, native)
Data Rate
(MB/s, native)
Bit Density
(Kbpi)
Track Density
(tpi)
Media Type
Media Length
Recording
Channels
Hardware Data
Compression
Interface
20
1.5
82.5
256
MP-2
1,800‘
2
Yes
SCSI-2/F
SE/HVD
DLT
4000
40
6.0
98.0
416
MP-2
1,800‘
4
Yes
SCSI-2/FW
LVD/HVD
DLT
8000
35
5.0
86.0
416
MP-2
1,800‘
4
Yes
SCSI-2/FW
LVD/HVD
DLT
7000
40
3.0
123.0
336
MP-2
1,800‘
2
Yes
SCSI-2/FW
LVD
DLT1
110
11.0
131.0
896
AMP
1,800‘
8
Yes
SCSI-2/FW
LVD/HVD
SDLT
220
Is there room for more new tape technologies? It seems unlikely. No
matter how well designed and well engineered a new tape technology
might be, it will require a significant new value proposition in order to
gain a foothold in the market.A new format would have to offer far
greater capacity or two to three times the speed of Quantum’s
DLTtape system in order to have a big impact.In reality,the new technologies challenge DLTtape technology in some areas, but not in all.
DLTtape technology also has a huge amount of “head room”in terms
of scalability and an extremely well defined technology road map.So
even if a new technology offers a short-term performance benefit
today, in all likelihood that advantage will disappear as the DLTtape
system continues to evolve.The new generation of DLTtape systems,
Figure 1-6 DLTtape Drive Comparison Chart shows some of the important speci-
fications for DLTtape systems, including the industry-leading Super DLTtape system.
THE EVOLVING TAPE STORAGE MARKET1.10
the Super DLTtape systems,leapfrog current and proposed competitive technologies,with first generation Super DLTtape products offering transfer rates of 11MB/s and capacity of 110GB,advancing to at
least one terabyte (uncompressed) over multiple generations (see
Chapter 17 for a product roadmap).
The biggest barrier to adoption of new tape formats is that users are
very reluctant to change backup technologies unless the benefits are
overwhelming and compelling.The pain involved in converting
archive tapes,for example, seems to be so acute that most people
don’t want to try it. So any new technology that is not backward/forward compatible can face an uphill battle to be widely accepted.
Today, DLTtape technology has a huge installed base,with over 1.5
million drives and over 55 million media cartridges shipped to customers.These facts,combined with a clear technology growth path
and a proven commitment to generation-to-generation compatibility,add up to an island of stability in a world of changing technology.
Range of Products
Another trend in the tape environment is user demand for a range
of compatible products that will address different performance,
functionality,and pr ice requirements. Users want a single solution
that works at many levels,not a different solution for every situation. Today,the DLTtap e system offers a very broad range of choices, ranging from stand-alone drives, to single-drive, multi-car tridge
autoloaders, to very large, enterprise-class libr aries w ith multiple
drives,multiple ports, and hundreds of cart ridges, all sharing compatible media, drives, and storage management software.
Ease of Use
Customers also want backup systems that are easier to use. In
response,the providers of backup solutions are starting to offer
bundled hardware/software solutions,w hich should lead to a
QUANTUM DLTtape HANDBOOK 1.11
happier “out of the box”experience for users. There is also a trend
toward providing more user-friendly graphical displays that show
the user exactly what’s going on w ith backup, where the process
stands at the moment, and what and where a hangup is occurring.
Application Diversity
Over time,the range of applications for tape is diversifying, and
that trend will probably continue.Tape, especial ly the DLTtap e
system,is not just about backup anymore.Tape applications also
include archiving, disaster recovery, hierarchical storage management, real-time backup,distribution (especially distribution of
video programs and graphics files), near on-line storage,and a host
of others.As these applications mature and become better defined,
you may see the emergence of different products to fit different sets
THE EVOLVING TAPE STORAGE MARKET1.12
Worldwide Re venue Market Share, 2000
Source: Dataquest, Preliminary Mar ch 2001
Exabyte 11
%
Sony 11
%
Quantum 78
%
Figure 1-7 The DLTtape System Is the Overwhelming Choice
among high-performance tape systems.
of needs. For example, we may see the emergence of a distinct class
of “desktop” DLTtape libr aries aimed at v ideo and g raphic ar ts
applications, while a class of mid-range to very large librar ies may
be targeted for Storage Area Network (SAN) applications.
The Last Word
In any discussion of the mar ket for DLTtape technology,the
bottom line has to be market share (see Figure 1-7).In 2000, the
total number of DLTtape drives in use g lobally was about ten times
what it was only four years earlier, and DLTtape dominates its
market space,with a market share of nearly 80%.
Next,we’ll look at what makes the DLTtape system uniquely
superior to other drive technolog ies.
QUANTUM DLTtape HANDBOOK 1.13
What Is the
DLTtapeSystem?
QUANTUM DLTtape HANDBOOK
2
2.1
In later chapters we will cover a great deal of technical information
about exactly how DLTtape system technology works. In this chapter
we focus on what it is about the DLTtape and Super DLTtape systems that makes them unique.When you examine the details,there
are dozens of differences between the DLTtape system and other
tape systems. In this chapter we stick to the major points.Some are
obvious, and some are invisible, buried inside the product.
Speed, Capacity,Reliability
From a performance point of v iew, the characteristics that distinguish the DLTtape system from other tape storage technologies are
speed, capacity,and reliability.When compared to other technologies (see Chapter 11 for a detailed analysis), current DLTtape and
Super DLTtape drives offer very fast transfer rates (11MB/s native),
DLTtape cartridges store large amounts of data (110GB on a sing le
Super DLTtape I cartridge), and DLTtape drives can run longer,
under more demanding duty cycles,than any competitive technologies. Or,as one DLTtape sytem user put it,“You take the specs
for the 8mm solutions we used previously and multiply by about
4x, and that gives you the DLTtape technology spec.”
WHAT IS THE DLTtape SYSTEM?2.2
Half-Inch Tape
The DLTtape system uses half-inch wide tape. That is the
widest tape available. The half-inch format was orig inally used in
mainframe products and was adopted by Digital Equipment
Corporation when they designed the ancestors of the DLTtape
system.What is important about the half-inch format is very
straightforward – it’s bigger than the other widely used technologies, such as quarter-inch, 4mm, and 8mm tape. Half-inch tape is
60 percent wider than 8mm tape. Therefore, you can put more
information on half-inch tape than you can on smaller-format tape.
Linear Recording,Versus Helical Scan
DLTtape drives read and write data in a linear pattern on the tape
(see Figure 2-2).That is, each data track goes the entire length of
the tape (about 1,800 feet for DLTtape IV and Super DLTtape I
media, for example). When data is being recorded,the first set of
tracks is recorded on the whole length of the tape. When the end
Cartridge
Head
Take-up reel
Head guide
assembly
Figure 2-1 Super DLTtape Drive delivers industry-leading
capacity, reliability, and data transfer rate in a 5.25" form factor.
QUANTUM DLTtape HANDBOOK 2.3
of the tape is reached, the heads are repositioned to record a new
set of tracks, and the tape is again recorded on its whole length,
this time in the opposite direction.That process continues,back
and forth, until the tape is full. Current DLTtape drives record
either 128 tracks (DLT 4000 drives), 168 tracks (DLT1 dr ives), 208
tracks (DLT 7000 and DLT 8000 drives), or 448 tracks (Super
DLTtape drives) on half-inch tape.
By contrast, helical scan systems record data in diagonal stripes
across the tape. This diagonal pattern allows data tracks to be overlapped for very high data density.One of the drawbacks of such
high density is the increasing difficulty it introduces in error detection and correction.Even a very small defect on a helical-scan tape
will probably corrupt the data, because such a large amount of
data is squeezed into a very small linear space.With DLTtape
Figure 2-2 The DLTtape System’s Linear Serpentine Recording
pattern writes data along tracks from one end of the DLTtape cartridge to
the other. Helical scan systems use read/write heads on a rotating drum to
record data in angled stripes across the tape.
Helical scan recordingDLTtape drive recording
media, however, a defect on the tape – say a scratch – could be as
long as an inch without causing an unrecoverable error. That’s
because the parallel channel architecture used in DLTtape drives
enables the system to automatically rewrite bad blocks to parallel
channels.
Maintaining Compatibility
Figure 2-3 shows the linear-serpentine recording pattern used in
DLTtape drives through the DLT 4000 model. The vertically-or iented pattern requires guard bands between tracks to prevent crosstrack interference.In the DLT 7000 and DLT 8000 drives (see Figure
2-4), data density was increased by angling the data pattern on
WHAT IS THE DLTtape SYSTEM?2.4
3mils
Track 0
Track 1
Track 2
Bottom edge of tape
Tape Direction
Figure 2-3 DLT 4000 Drive writes data on two channels simultaneously
in linear tracks that run the length of the tape. The system has a capacity of
20GB native and 40GB compressed.
1.75mils
Bottom Edge of Tape
Track 3
Track 2
Track 1
Track 0
Track 4
Tape Direction
Figure 2-4 DLT 7000 and DLT 8000 Drives’ Symmetric Phase
Recording
™
writes data in an angled pattern, allowing higher data
density, with per cartridge capacity of 40GB native and 80GB compressed.
QUANTUM DLTtape HANDBOOK 2.5
Head Motion
Write Heads Write Heads
Read Heads
Figure 2-6 DLT 7000 and DLT 8000 Read/Write Head features 4
channels for a data transfer rate of up to 6MB/s (native). Center row of read
elements provides read-after-write data accuracy.
Figure 2-7 Super DLTtape Read/Write Head features 8 channels.
Very small Magneto-Resistive Cluster (MRC) Heads yield data transfer rates
as high as 11MB/s (native).
Head Motion
Write Heads Write Heads
Read Heads
Figure 2-5 DLT 4000 Read/Write Head writes data with the tape
running either forward or backward, and performs a read-after-write in
either direction to ensure accuracy.
WHAT IS THE DLTtape SYSTEM?2.6
adjacent tracks. This data recording technique is called Symmetric
Phase Recording™(SPR). SPR’s her r ingbone pattern eliminates the
need for guard bands and thus allows greater track density.
Figures 2-5 and 2-6 show the arrangement of read/write elements on
the two-channel DLT 4000 heads and the four-channel DLT 7000 and
DLT 8000 heads.When reading DLTtape cartridges recorded on earlier
models,the DLT 7000 and DLT 8000 read/write heads automatically
shift to a vertical orientation.This feature provides backward compatibility and protects the end user’s investment in the DLTtape system.
Figure 2-7 shows the read-write head assembly for the Super DLTtape
drive.Super DLTtape drives incorporate newly designed MagnetoResistive Cluster (MRC) heads. This design features clusters of very
small,cost-effective magneto resistive tape heads,densely packed in a
small area on the head.MRC heads deliver higher data transfer rates
and greater data density than traditional heads of similar size.They are
also less susceptible to negative effects due t o environmental (temperature and humidity) conditions.
Simpler Tape Path
The design of the head guide assembly (HGA) is at the heart of what
makes DLTtape technology superior (see Figure 2-8).More than any
other characteristic,it is what makes a DLTtape drive a DLTtape drive.
It is a patented design,and it is one of the keys to the success of the
DLTtape system.
The head guide assembly positions the tape in front of the selfcalibrating read/write heads. The DLTtape system HGA is different
from competing technologies.On 4mm and 8mm helical scan systems (see Figure 2-12),the head guide systems are designed to
move.These systems must reach out,hook the tape, wrap it
around the rotating read/write drum,hold it in position, and then
move the tape back into its cassette.(See Figure 2-12.)
QUANTUM DLTtape HANDBOOK 2.7
Drive
Leader
Head
Take-up
Reel
Tach
Assembly
Figure 2-8 The Patented DLTtape Head Guide Assembly, first
incorporated in the TF85 drive, is one of the keys to DLTtape reliability.
Six precision rollers provide a gentle tape path for long tape life.
Take-up
Reel
Head Guide Rollers
Head
Drive
Leader
Figure 2-9 The Super DLTtape Head Guide Assembly is a refined
version of the DLTtape Head Guide Assembly. It incorporates only four
rollers, further reducing contact and tape wear.
WHAT IS THE DLTtape SYSTEM?2.8
Figure 2-11 Super DLTtape System Tape Path is even sim-
pler than that of the DLTtape drive, requiring only four precision
rollers to guide the tape.
Figure 2-10 DLTtape System Tape Path Is Key reason for
the industry-leading reliability, long life, and accuracy of DLTtape
technology. Six precision rollers guide tape to internal take-up reel.
QUANTUM DLTtape HANDBOOK 2.9
Figure 2-12 Helical Scan Tape System must pull tape out of
the cartridge and around a spinning read/write head. Acute wrap
angles and recording-side contact reduce tape life.
By contrast,the DLTtape head guide assembly is entirely different. It
remains stationary.It consists of a series of six precision rollers.
Instead of grabbing the tape in the middle and pulling it into place,
as with helical scan systems, the DLTtape guide system links a leader
strip on the end of the tape and pulls it out of the car t ridge, guides it
around the head guide assembly in a smooth arc,and gently wraps it
around the take-up reel in the drive.The rollers guide, but do not
pull the tape. The wr ap ang les around the guide rollers are gentle.
Contact between tape and guide is minimized.The recorded side of
the tape never touches the guides,minimizing tape wear.The head
guide assembly in the Super DLTtape drives is a refined design that
incorporates only four rollers,reducing even further the amount of
contact with the tape.
WHAT IS THE DLTtape SYSTEM?2.10
Single Reel Design
The DLTtape media cartridge is unique in the midr ange system
market, in that it has only one reel. The take-up reel – the second
reel – is in the DLTtape drive itself.This single-reel design leaves a
great deal more space for tape inside the cartridge. (See Figure 2-13
and 2-14.)
Most tape cassettes have two reels – a feed reel and a take-up reel.
The tape is pulled across the read/write heads between the two
reels, kept in alignment by the moving head guide assembly
described earlier.So, the par t of the tape that needs to be accurately aligned with the read/write heads is actually suspended between
two moving points, held in place by a series of movable guides. All
that motion makes it hard to maintain perfect alignment.
On the other hand, the DLTtape media is attached at one end to a
fixed point,the take up reel,w hich is mounted within the drive
Figure 2-13 DLTtape Cartridge provides low-cost-per-giga-
byte, high density data storage. Single-reel design eliminates
wasted space.
Access door Leader Supply reel
Write
Protect
switch
Tape
Drive access
itself, and it is guided by the stationary HGA. It is inherently more
stable, because much less movement is possible.
When you look at a conventional two-reel 8mm cassette, it is obvious that the two reels take up a great deal of space, leaving less
space for tape. Not only can you see the difference, you can feel it.
A DLTtape cartridge, with only one reel, is packed full with tape.
Just pick up a DLTtape cartridge, and you realize that it is heavy,
because it is all storage, and very little empty spaces.
These characteristics – half-inch format, linear recording, patented
tape guide, and the DLTtape car tr idge – are some of the keys that
make DLTtape technology clearly superior.
Next,we look at the history of the DLTtape technology.
QUANTUM DLTtape HANDBOOK 2.11
Figure 2-14 The Super DLTtape I Cartridge is a ruggedized
design that includes an internal circular wall and ribbing, along
with new wear-resistant materials to reduce the generation of
debris.
History of
DLTtape Technology
QUANTUM DLTtape HANDBOOK
3
3.1
In 1984, the Berlin Wall was still standing, and the real estate bust,
Black Monday, recession, and the collapse of the minicomputer
market were still years away. At home, Commodore 64 and Atari
computers were selling well.On the IS front, the Apple Macintosh
and the 80286 PC/AT were introduced and began to complicate life
in the glass house.
In 1984,Digital Equipment Corporation was on a roll,capturing
midrange and mainframe market share with its networked minicomputers.Digital’s MicroVAX II workstation system was nearly ready for
release,but it needed a backup system.A group of Digital storage engineers,led by consulting engineer Fred Hertrick, worked day and night
to come up with a drive that could match the M icroVAX performance.
With time short and the pressure on,the group decided to use off-theshelf half-inch magnetic tape,the same kind of stock used in mainframe-class reel-to-reel systems.Hertrick and his team devised a drive
that combined the qualities of reel-to-reel and cartridge tape systems.
No Take-Up Reel
The new system used a square cartridge that contained tape, but
no take-up reel.The take-up reel was built into the drive itself.
This design eliminated the wasted space typically associated with
cassette and cartridge drives such as the QIC, 8mm, and v ideo cas-
HISTORY OF DLTtape TECHNOLOGY3.2
sette systems (DAT wasn’t out yet).Of course,the drive itself had
to be made somewhat larger than most to accommodate the internal take-up reel.Dubbed the TK50, the new tape drive was capable
of storing 94MB per cartridge.
Using a ferrite read/write head,the TK50 recorded data in linear
blocks along 22 tracks using two channels.The TK50’s read/write
head actually contained two sets of read/write elements. One set
was used when reading and writing forward and the other reading
and writing backward. The TK50 started recording at the beginning of the tape, recording on one track.When it reached the end,
the system recorded back to the beginning along a new track. After
every two tracks were written, the system moved the head up the
width of one track and began the process again. The read-afterwrite capability of the system ensured basic data accuracy.
The TK50 was introduced with the MicroVAX II in 1985.The drive
fit into a full height, 5.25" drive bay in the MicroVAX.Compared
to the DLTtape drive of today, the TK50 was like Neanderthal Man
– it walked upright and used tools, but it still had a long way to go.
The TK line of drives used only two guide rollers to hold the
streaming tape against the read/write head. This was okay for the
low data densities of these early systems, but would never work at
the extreme densities we’ve come to expect today.
In 1987,the year of the first IBM 80386-based PCs and Windows
2.0, Digital rolled out the TK70. This new tape drive offered 294MB
of storage on the same square tape cartridge, a 3x improvement
over the TK50.This was accomplished by upping the number of
tracks to 48 and increasing density on the same half-inch tape.
Millions of PCs were in use and had become a permanent part of
corporate America.Popular PC applications included desktop publishing, word processing, spreadsheet, and database management.
QUANTUM DLTtape HANDBOOK 3.3
Macintosh and its GUI operating system were growing in popularity,having entered through the back door of corporate gr aphics
departments and in-house advertising groups.
Need for Precision
The TK70 wasn’t enough to quench the thirst for greater storage
capacity and faster throughput speed in tape backup systems.Disk
drive capacity was steadily increasing.Industry was becoming
more dependent than ever on information systems technology.
Databases swelled to overflowing, and tape dr ives lagged behind
the growing wave.
The storage systems engineers knew that, in order to push the
envelope,the y’d have to improve the precision of the tape guide.
Unless the tape was held rock solid in front of the read/write head,
there was little hope of achieving the quantum leap that was needed in tape capacity.
By 1988,digital audio tape (DAT) was about to cross over from the
music world to become the smallest entry in data storage subsystems.However, though small in size, these systems were projected to
store at least a gigabyte (GB) or more.Eight millimeter and VHS
video/data systems were already offering storage capacities of 2GB or
more.Clearly the engineers had some serious work to do.
And, they did it. In 1989, Digital introduced the TF85,the first true
DLT system. The TF85 (later to be dubbed the DLT 260) incorporated a host of new features that enabled the system to pack
2.6GB onto a 1,200 foot tape (CompacTape
™
III, now known as
DLTtape III). Less than two years after the introduction of the
294MB TK70, the engineers had increased storage capacity nearly
tenfold and made a breakthrough in tape drive performance that
we now call DLTtape technology.
Head Guide Assembly
Probably the most important new feature introduced with the
TF85 was the patented six-roller head guide assembly (HGA).This
mechanism provides a gentle,solid path to precisely move the tape
past the read/write head. This boomerang-shaped assembly consists of a forged aluminum base with six precision rollers fixed to
it. The new HGA enabled the engineers to safely increase track
density from 48 tracks to 128 tracks across the half-inch wide tape.
The six-roller head guide assembly (see Figure 3-1) gave the TF85
a much shorter tape path than helical scan systems like the 8mm
drive,which meant less wear and tear on the tape.The rock solid
platform of the HGA also provided the industry’s most accurate
tape path. Helical scan systems have to draw tape around a spinning read/write drum, which requires a moving tape path with
many more parts and points of tape wear.
Write/Read/Write
Another innovation in the TF85 resulted in high performance data
transfer speed and improved error correction.The read/wr ite head
was equipped with an additional write element. The elements now
were arranged in a write/read/write pattern, allowing continuous
accuracy checking. This pattern enabled the TF85 to read after
writing on two channels and in both forward and reverse.Multichannel serpentine recording was born.
Seven-Cartridge Autoloader
To meet the need for unattended backup of large databases, Digital
also introduced a seven-cartridge autoloader,designated the TF857.
This system used a single TF85 drive, a seven-cartridge magazine,
and an elevator mechanism. Tape loaders and librar ies minimized or
eliminated operator involvement and simplified tape management.
HISTORY OF DLTtape TECHNOLOGY3.4
In 1991,Windows 3.1 became a standard for PCs.“Mini”manufacturers industry-wide felt the pressure as companies discovered that
a string of inexpensive PCs could be networked to do the same
work that had once been the province of the minicomputer.
Meanwhile,Dig ital’s storage group kept advancing DLT technology.In 1991, the company introduced the TF86 (later dubbed
the DLT 600), which offered 6GB of storage on the same 1,200'
DLTtape III (known at the time as CompacTape III) cartr idge.
This new drive was read/write compatible with the TF85, preserving customer investment in drives and media.
Two years later, the company introduced the TZ87,now known as
the DLT 2000 tape drive. This advanced system offered 10GB of
native capacity on a single CompacTape III cartridge (now known
as DLTtape III), 2MB of read/write data cache memory,and a data
transfer rate of 1.25MB/s. In 1993,Digital also introduced a compact five-cartridge tape loader (now known as the DLT 2500) that
Drive
Leader
Head
Take-up
Reel
Tach
Assembly
Figure 3-1 The Patented DLTtape Head Guide Assembly, first
incorporated in the TF85 drive, is one of the keys to DLTtape reliability.
Six precision rollers provide a gentle tape path for long tape life.
QUANTUM DLTtape HANDBOOK 3.5
could store up to 50GB of uncompressed data using the
DLT 2000 drive and eventually up to 100GB of uncompressed
data using the DLT 4000 drive.
Early in 1994, Digital began to gear up to sell DLT tape drives outside its normal user base. The SCSI-2 interface used by DLT drives
was an industry standard that would allow almost any computer to
work with the drives.At about this time,Digital renamed its disk
and tape subsystem group Avastor.
Quantum Enters the Picture
By 1994,Quantum Corporation, a Milpitas, California-base d maker
of high performance disk drives since 1980, had built a healthy $2.1
billion business. The company was the leading supplier of 3.5-inch
hard drives for PCs and the third leading supplier of hig h-capacit y
drives (2GB and up).In DLT technology,Quantum saw the opportunity to acquire advanced technology that could ensure the company’s leadership position and op en new markets for it. Quantum
acquired Digital’s disk and tape divisions and, within them, DLT
technology .
Potential for Success
Quantum recognized the undeveloped potential that DLT technology represented.This technology was the perfect complement to
their established disk drive business.Almost immediately,Quantum
announced new tape drives based on the acquired technology. In
late 1994,Quantum rolled out the DLT 4000 drive and leapt to the
head of the line in performance, capacity and reliability.
By increasing areal density (bits per inch) from 62,500 to 82,000
and tape length by 600 additional feet (to 1,800 feet),Quantum’s
storage engineers were able to up the capacity of the DLT 4000 system to 20GB (40GB compressed) on a single half-inch DLTtape IV
HISTORY OF DLTtape TECHNOLOGY3.6
cartridge. The new DLTtape system provided data transfer at
1.5MB/s (3MB/s compressed) and was fully read/write compatible
with previous generations of DLTtape drives.Again,customer
investments in DLTtape drives and media were preserved.
Sales Growth
Quantum sales rose to $3.5 billion for FY’95 on strong growth on all
fronts.Quantum had evolved from its role as only a disk drive maker
to a provider of mass-storage solutions. The r apid r ise of multimedia,
data warehousing,data mining, large network storage servers,
Internet/Intranet growth,and 7x24 information system operations
meant the need for fast,high capacity backup systems was exploding,
and Quantum had the products that the market wanted.
In 1995,Quantum introduced an improved DLT 2000 system,
dubbed the DLT 2000XT for “extended tape.”The new system provided an additional 5GB over the capacity of the DLT 2000 drive for
a total of 15GB native capacity. Quantum was able to achieve this
improvement through firmware changes (see Chapter 15),and by
increasing the length of the tape used from 1,200 to 1,800 feet
(DLTtape IIIXT).As usual,the DLT 2000XT was fully backward compatible with all previous DLTtape drives.
Others Playing Catch-up
Quantum enjoyed a time-to-market gap that had manufacturers of
8mm, DAT, and QIC tap e drives scrambling to tr y to match
DLTtape system capacity and performance. Just when it seemed
they might come close, Quantum introduced the DLT 7000 drive in
1996. This new drive offered a total storage capacity of 35GB native
(70GB compressed) on the 1,800 foot DLTtape IV cartridge.
Thanks to the DLT 7000 drive’s new 4-channel head, it could
transfer data at the rate of 5MB/s in native mode. Other tape
QUANTUM DLTtape HANDBOOK 3.7
drive makers were left far behind. Demand for the drive quickly
outstripped supply as OEMs and resellers flocked to take it on.
Library manufacturers wanted the drive in order to up total
library capacities into the multi-terabyte range. Unix Review
magazine named the DLT 7000 drive one of its Outstanding
Products for 1996.Press accounts began by stating the DLT 7000
drive’s technical dominance at the high end of the midrange tape
backup market.
DLT 8000 Drive
In 1999, Quantum introduced the DLT 8000 drive, a significant
step up in performance and capacity over the market-leading
DLT 7000 drive. The DLT 8000 system delivered a 15% increase in
storage capacity (from 35GB to 40GB native),a 20% increase in
transfer rate (from 5MB/s to 6MB/s), and an important improvement in reliability (from 200,000 hours MTBF to 250,000 hours).
And, of course, the DLT 8000 system delivered another important
0
200,000
400,000
600,000
800,000
1,000,000
1,400,000
1,200,000
1,800,000
1,600,000
70,000,000
60,000,000
50,000,000
40,000,000
30,000,000
20,000,000
10,000,000
0
FY 97 FY 98 FY 99 FY 00 Q3FY 01
Source: Quantum Corporation
Units, Drives Installed Units, Media Shipped
Figure 3-2 The Installed Base of DLTtape systems has grown dramatically,
with a projected total of over 1.5 million drives installed and over 55 million cartridges shipped to customers by the end of Q3, FY01.
HISTORY OF DLTtape TECHNOLOGY3.8
benefit – investment protection: the DLT 8000 drive,which uses
the same DLTtape IV tape cartridges as the DLT 7000 drive,is
compatible with a very large percentage of all of the DLTtape
media ever sold (some 55 million cartridges).
DLTtape System Sales Growth
At the end of FY '99,sales of DLTtape products hit $1.4 billion, and
DLTtape products accounted for nearly 30 percent of Quantum’s
sales.According to Quantum CEO Michael Brown,“The move to
enterprise servers, the proliferation of Internet servers, and the
increase in mission-critical content stored on these servers have
dramatically increased the demand for backup and archival storage.
Quantum’s DLTtape drives use advanced linear recording technology and a highly accurate tape guide system to provide exceptionally
reliable,scalable data backup and archival storage for mid-range
and high-end systems. These drives, which have become the industry’s de facto standard, provide a strong foundation for market
acceptance of our next generation products.”
The Next Generation: Super DLTtape Technology
Early in 1998, Quantum had also revealed plans from the most
important development in the history of DLTtap e technology:
Super DLTtape technology,the next generation of DLTtape technology.It incorporates dramatic advances in virtual ly ever y impor tant
area,from mechanical packaging through head design, tape guidance,and media properties.Yet the Super DLTtape system is also
unmistakably a DLTtape product, providing a smooth growth path
from today's market leading technology to a new technology that
will deliver order-of-magnitude advances in capability.
By mid-2000, Quantum announced plans to deliver a family of
competitively priced tape drive products based on Super DLTtape
QUANTUM DLTtape HANDBOOK 3.9
technology.Volume production and first customer shipments began
in Q1, 2001. These products address the individual storage needs of
low-,mid-, and high-end customers in the mid-range data storage
market.These new products include drives that deliver capacities of
110GB (uncompressed),and transfer rates of 11MB/s (uncompressed).They are the first products based on the Super DLTtape
technology, a technology that Quantum will continue to evolve,
with coming generations planned to deliver over 1 terabyte of
storage (uncompressed) on a single cartridge. And, of course, the
Super DLTtape system delivers another and continuing benefit –
investment protection.The Super DLTtape system is backward read
compatible with DLTtape IV cartr idges wr itten on DLT 4000,
DLT1, DLT 7000, and DLT 8000 drives.
DLT1 Drive
Early in 2001, Quantum introduced the DLT1 drive. Delivering
40GB per cartridge native capacity (80GB compressed), along with
a native transfer rate of 3MB/s (6MB/s compressed),the DLT1 drive
is an exceptionally cost-effective backup solution for a wide range
of applications. The DLT1 can back up most small- and mediumsize storage servers and workstations on a single cartridge. Available
for both internal installation and as a free-standing, table-top unit,
DLT1 is designed primarily for stand-alone applications. It uses the
same DLTtape IV cartr idge that is standard for the DLT 4000 drive,
allowing users of small and medium-size storage devices and workstations a simple migration path and the ability to make an initial
investment in their future storage strategy using the DLTtape products.
Next,we’ll take a look at the advantages that make the DLTtape
system the most sought after backup solution on the mar ket today.
HISTORY OF DLTtape TECHNOLOGY3.10
Why Customers
Want DLTtape Systems
QUANTUM DLTtape HANDBOOK
4
4.1
When Quantum bought DLT technology in 1994, sales of DLT
products were running a modest 20,000 units per year. In just six
years, DLTtape drive sales climbed to over 500,000 units a year.
Why are so many people buying DLTtape systems? Some of the
reasons have to do with big industry trends. Others have more to
do with the basics of DLTtape technology itself. In this chapter,
we’re going to look at the forces that are driving customer
demand for DLTtape system b ackup solutions.
The Server Boom
One of the industry trends driving the demand for DLTtape systems is the growth in the population of midrange servers. Not
many years ago, 8mm and 4mm DAT (digital audio tape) dominated the backup world.There was no reason to think that wouldn’t
continue.Many people probably assumed they would keep using
DAT for backup until optical disk technology eventually took over.
And, in the desktop computer world,that scenario is holding up
pretty well. People are still buying 4mm DAT drives by the tens and
hundreds of thousands, and optical – in one form or another – is
coming up over the horizon.
The midrange field, however, offers a whole different scenario.
Instead of the “death of the minicomputer industry,”we have seen
WHY CUSTOMERS WANT DLTtape SYSTEMS4.2
the “birth of the ser ver industry.”Of course, today’s servers look a
great deal like yesterday’s minicomputers,and, instead of disappearing, this class of computers is growing very rapidly.
These midrange servers support much larger disk storage than
desktop systems.That means you need more backup capability –
more capacity, more speed, and greater reliability.These backup
needs are the strengths of the DLTtape system. It’s no accident that
the growth in popularity of the DLTtape system closely parallels
the boom in server use.
The “Mission Critical”Boom
Much of the growth in the midrange market is fueled by a new
class of mission critical applications, such as Internet servers,
enterprise wide email servers, v ideo editing, electronic commerce,
and so on. These applications demand bigger disks, more capacity,
and, of course, better backup solutions. This is where DLTtape
technology really shines.
Customers are buying DLTtape systems because these mission critical applications need backup solutions that offer more speed,
capacity,and reliability: exactly what DLTtape system backup delivers. Don’t forget that DAT (digital audio tape) and 8mm are really
consumer entertainment technologies,adapted for industrial use.
DLTtape technology is industrial-strength from the start. It just
takes one failure of a mission cr itical application to make people
understand that what they really need is industrial strength backup.
A Proven Technology
“Leading edge”technologies sometimes end up on the “bleeding
edge.”In this case,however, DLTtape technology is growing so fast
because it has been proven.People want DLTtape technology
because they know it works.Today,there are over 1.5 million
QUANTUM DLTtape HANDBOOK 4.3
DLTtape drives installed,and over 55 million DLTtape cartridges in
use worldwide.In the understated words of one user,“DLTtape
technology is a well understood way to get a lot of data backed up.”
Widely Available
DLTtape systems are available from many sources.The list of
OEMs who put DLTtape drives in their systems is impressive and
growing. Almost all the leading vendors of mid-range computer
systems or workstations sell DLTtape products, including Compaq,
Dell, Hewlett-Packard,IBM, and Sun.Every one of these manufacturers offers DLTtape systems as factory installed backup systems
and libraries for their high-performance ser vers.
DLTtape technology is also available from the leading manufacturers of tape storage libraries and autoloaders. DLTtape products are
available through major industrial distributors, and from valueadded resellers,many of whom serve specialized markets.A good
example is Avid Technolog y,the leader in special effects editing
systems for film and video; DLTtape drives come as standard
equipment with Av id systems.
Speed Is Critical
Industry trends and good history have created the conditions for
success of DLTtape technology.However,trends don’t mean much
if the technology doesn’t deliver performance.Customers want
DLTtape technology because it offers blazing performance.
DLTtape dr ives are very fast: from 1.5MB/s to 11MB/s in “native”
or uncompressed mode (see Figure 4-1).That’s nearly hard disk
drive speed. If you are running a network in a large engineering
department, and all the ser vers must be backed up between midnight and 6 a.m., speed is your best friend. Or, if you’re putting the
finishing touches on special effects for a TV commercial,and the
clock is running out, you don’t want to have to face the long, slow
process of putting the ad on tape before you can ship it to the
client.You want DLTtap e system speed.
Bigger Is Better
Users want DLTtape technology because bigger is much better.You can
put much more information on half-inch-wide tape than you can on
8mm or 4mm tape.Currently, an SDLT 220 drive can store 110GB on
a single Super DLTtape I cartridge.Add compression of 2-to-1 and
you’ve got 220GB on one four-inch-square cartridge (not to mention
22MB/s throughput).That’s enough capacity to store multiple fulllength feature films,and you can look for greater capacity in the future
(see Chapter 17 for details on Super DLTtape technology).For the typ-
WHY CUSTOMERS WANT DLTtape SYSTEMS4.4
Figure 4-1 DLTtape Drive Comparison Chart shows some of the important
specifications for DLTtape systems, including the industry-leading Super DLTtape system.
Capacity
(GB, native)
Data Rate
(MB/s, native)
Bit Density
(Kbpi)
Track Density
(tpi)
Media Type
Media Length
Recording
Channels
Hardware Data
Compression
Interface
20
1.5
82.5
256
MP-2
1,800‘
2
Yes
SCSI-2/F
SE/HVD
DLT
4000
40
6.0
98
416
MP-2
1,800‘
4
Yes
SCSI-2/FW
LVD/HVD
DLT
8000
35
5.0
86
416
MP-2
1,800‘
4
Yes
SCSI-2/FW
LVD/HVD
DLT
7000
40
3.0
123
336
MP-2
1,800‘
2
Yes
SCSI-2/FW
LVD
DLT1
110
11.0
131
896
AMP
1,800‘
8
Yes
SCSI-2/FW
LVD/HVD
SDLT
220
ical system administrator running a network backup application,more
capacity per cartridge means less need to swap cartridges.
More Reliable
While we were researching this book,we talked to end users and
network managers. Over and over again,they told us that they had
switched to DLTtape backup because the systems they had been
using just weren’t reliable enough anymore. Under the pressure of
backing up big networks,4mm and 8mm solutions just don’t cut it.
This from the people whose necks are on the line when systems fail.
They say things like “too many midnight calls,” or “ever y once in
a while an 8mm drive would go bang,”or “our old 4mm drives
could not handle it.”So,customers want DLTtape technology
because it is more reliable than any other backup technology.
Heavy Duty
Most drive makers base their performance and reliability figures on
drive utilization (duty cycle) as low as 10 percent.That means that
in a 7x24 operation, other drive makers base reliability figures on as
little as 2.5 hours of use during every 24-hour period. At Quantum,
we have traditionally calculated our reliability figures based on 100
percent usage.In fact,even at 100 percent duty-cycle,DLTtape drives are rated at up to 250,000 hours Mean Time Between Failures
(MTBF). Even when compared to a competing drive offering the
same MTBF, DLTtap e drives are the clear winner,because we have
calculated MTBF assuming 100 percent usage.In practice,few drives will actually be subjected to non-stop operation. But, it’s nice to
know you could run your DLTtap e drive continuously if you had
to,w ithout the worry of premature failure or data loss.(See
Chapter 5 for a complete discussion of DLTtape system reliability.)
Economy
Because DLTtape technology star ted life as a proprietary technology,and because its market is primarily in the midr ange and high-
QUANTUM DLTtape HANDBOOK 4.5
end server arena, some people mistakenly characterize DLTtape
technology as expensive.That is simply not the case.
One of the great things about the free market is that buyers usually
figure out the best deals pretty quickly.Users want DLTtape technology because, as it turns out, in many applications, not only does it
offer superior performance, but it’s also the least expensive way to
get the job done.
DLTtape technology isn’t the cheapest backup for desktop applications – yet. That’s still 4mm DAT. But once you jump to UNIX
workstations or enterprise networks, it’s a whole different story.
For starters,you need to factor in capacity. At 40GB uncompressed, for example, the DLT 8000 drive compares favorably in
price with competitive units of lesser capacity.
The cost equation changes when you factor in performance.If you’ve
got all night and you only need to backup a few files,slow is fine. But,
if you’re try ing to back up a large, constantly changing database, and
the only time you can do it is from 2 a.m.to 5 a.m., then speed is
money.For more and more applications,with growing storage needs
and shrinking backup windows,the critical issues are: Can you complete this backup in the available time,w ith minimum operator
involvement, and provide maximum dependability? With its 110GB
capacity and 11MB/s native transfer rate,the SDLT 220 drive is the
value leader in these increasingly common circumstances.
Comparing media cost is a similar story.If your total system storage
capacity is only one or two GB,smaller capacity,lower-initial-cost
tape cassettes may be fine.As soon as you jump up a class and have 5,
10,30GB or even terabytes to back up,dollars-per-gigabyte becomes
the meaningful measure of the cost of media. Gener ally,the larger
your backups are,the more cost-effective it becomes to use DLTtape
WHY CUSTOMERS WANT DLTtape SYSTEMS4.6
technology.No other tape drive system packs as much data in a single
cartridge as the DLTtape system; up to 110GB in native mode on a
single Super DLTtape I cartridge.
True Cost
The true cost of backup isn ’t in the drives and the media at all – it’s in
the people and time it takes to meet your backup goals.If files are small
and the windows of time are wide open,administrative costs probably
aren ’t even worth measuring.In these rare situations,the lowest initial
cost solution works.As soon as you crank up the volume,however,
administrative costs can soar. If you’ve got 4mm cassettes filling up constantly,just swapping tapes can become a time sink.And if you’re really
pushing the limits of speed,capacity ,and duty cycle of your backup
solution,failure rates start climbing. That means serious interruptions
and delays as you scramble to replace bad drives. In other words,
administrative costs quickly get out of control.One user told us he used
to spend 35 hours a week to support 4mm DAT backup for critical
client files.When he moved to DLTtape backup,that cost virtually disappeared.That’s another reason why people want DLTtape technology.
Scalability
One of the primary reasons people want DLTtape technology is scalability.Scalability means DLTtape system customers solve the backup problem once,and then keep applying the same solutions as
needs grow.You can go from a DLT 4000 dr ive with uncompressed
capacity of 20GB, to an SDLT 220 drive with uncompressed capacity
of 110GB.Beyond that, you can move up to one of many available
automated DLTtape libraries with capacities r anging from “a terabyte on a desktop”to many terabytes or even petabytes on the floor.
Room t o Gr ow
One of your goals should be to pick a backup technology that has
a future.While helical scan technologies,for example, are pushing
QUANTUM DLTtape HANDBOOK 4.7
the upper limits of their potential,DLTtape technology is just hitting its stride, w ith plenty of room to grow.
Half-inch tape simply offers more growth capacity than the much
smaller 4mm or 8mm formats (see Figure 4-2).Where 8mm and 4mm
are pushing their density limits,half-inch DLTtape technology isn’t even
close to maxing out.For example, the DLT 4000 drive uses 128 recording tracks.The DLT 8000 drive uses the Symmetric Phase Recording
™
pattern,allowing it to lay down 208 tracks on the same half-inch tape.
The next generation of Super DLTtape systems increased track density
yet again,by a factor of more than 2X, to 448 tracks.
Track density is just one parameter.Another is the underlying tape
technology.Today, DLTtape IV cartridges use metal particle (MP)
media.Super DLTtape I cartridges use state-of-the-art Advanced
Metal Powder (AMP) media. AMP media offers increased media
capacity,ease-of-use, and lower cost of ownership.Designed to meet
the needs of multiple generations of Super DLTtape drives,AMP
DAT QI C-MC QIC-DC 8mm Half-inch DLTtape
0
2,000
4,000
6,000
8,000
10,000
DAT QIC-MC QIC-DC 8mm
Media Recording
Area (square inches)
Figure 4-2 Half-inch DLTtape Media leaves plenty of room
for capacity growth for future DLTtape drives. A single DLTtape
cartridge has a tape area of over 10,000 square inches.
WHY CUSTOMERS WANT DLTtape SYSTEMS4.8
media ensures the highest track density available today. AMP uses
durable metal powder technology for recording at very high densities.
The back side of the AMP media contains specially formulated backcoating to receive the optical servo tracks,so customers can reserve
the entire data-bearing side of the media for recording data and eliminate the need for pre-formatting.
DLTtape System Compatibility
In most cases,IS managers are reluctant to change backup technology.
You may have dozens,hundreds,or even thousands of old backup
QUANTUM DLTtape HANDBOOK 4.9
Figure 4-3 Backward Compatibility is maintained throughout the DLTtape media
family .
Tape Type
(recorded on
drive type)
DLTtape IIIXT
(recorded on
DLT 2000XT)
DLTtape IV
(recorded on
DLT 4000)
DLTtape IV
(recorded on
DLT 7000)
DLTtape IV
(recorded on
DLT1)
DLTtape IV
(recorded on
DLT 8000)
Super DLTtape I
(recorded on
SDLT 220)
15GB
20GB
35GB
40GB
40GB
110GB
1.5MB/s
1.5MB/s
1.5MB/s
1.5MB/s
1.5MB/s
NA
Native
Capacity
Native
Transfer
Rate
(read
on DLT
4000)
Native
Transfer
Rate
(read
on DLT
7000)
Native
Transfer
Rate
(read
on DLT1)
Native
Transfer
Rate
(read
on DLT
8000)
Native
Transfer
Rate
(read
on SDLT
220)
1.5MB/s
1.5MB/s
5MB/s
NA
5MB/s
NA
NA
1.5MB/s
NA
3MB/s
NA
NA
1.5MB/s
1.5MB/s
5MB/s
NA
6MB/s
NA
NA
1.5MB/s
3.5MB/s
3MB/s
4MB/s
11MB/s
NA=Tape format is not compatible with the tape drive.
tapes.You w il l never need most of them. But if you do need some old
tapes from last year, or 5 years ago, or just last week,you would have
a major problem if you had changed backup platforms. That is generally not the case with DLTtape technology.A cartr idge recorded on
a DLT 2000 drive three or four years ago can be read on a DLT 4000
drive today.You can put a DLTtape IV cartridge in a DLT 4000 drive
today, fill it w ith data, and two years from now you will be able to
read it on a DLT 8000 drive (see Figures 4-5 and 4-6).All DLTtape
drives up to the DLT 4000 drive use a similar head design and recording pattern that makes possible compatibility among drives.
However, the DLT 7000 and DLT 8000 drives use a new recording
pattern,Symmetric Phase Recording.T he read/wr ite head of the
DLT 7000 and DLT 8000 drives tilt forward and back (see Figure 4-5)
to achieve higher track density.When a DLTtape cartridge that has
been recorded on a DLT 4000 drive,for example, is inserted in a
DLT 8000 drive,the drive automatically detects the difference in
recording pattern.The DLT 8000 drive then automatically adjusts its
read/write head (Figure 4-6) to a vertical position that enables it to
read the older DLTtape cartridge.
WHY CUSTOMERS WANT DLTtape SYSTEMS4.10
Forward
Write Cores
Reverse
Write Cores
Reader Cores
Figure 4-4 DLT 7000/DLT 8000 Read/Write Head tilts
back and forth to record at highest data density, yet it can still read
older formats by assuming vertical position shown here.
QUANTUM DLTtape HANDBOOK 4.11
Figure 4-5 Symmetric Phase Recording (SPR), used in
DLT 7000 and DLT 8000 drives, angles recording tracks to prevent
cross-track interference and increase data density.
Figure 4-6 DLT 7000/8000 Head Positioned to read
DLTtape cartridge recorded on an older DLTtape drive, providing compatibility and data interchange.
Forward Tape Direction
Reverse Tape Direction
Forward Tape Direction
Reverse Tape Direction
WHY CUSTOMERS WANT DLTtape SYSTEMS4.12
The DLT1 drive uses DLTtape IV media, so DLT1 drives can read
any DLTtape IV cartridges recorded on DLT 4000 drives.And,of
course,DLTtape IV cartr idges recorded on DLT1 drives can be read
by DLT 4000 drives and by SDLT 220 drives.
Super DLTtape I Media Compatibility
Super DLTtape I media provides backward read compatibility
with DLT 4000, DLT1, DLT 7000, and DLT 8000 drives using
DLTtape IV cartridges. To read DLTtape IV cartridges recorded
on a DLT 4000 drive or DLT1 drive, the Super DLTtape Backward
Read Compatible head remains in an upright position. To read
DLTtape IV cartridges recorded on a DLT 7000 or DLT 8000 dr ive,
the Super DLTtape head tilts to read data recorded using Sy mmetr ic
Phase Recording (SPR).(See Figure 4-7.) That means data wr itten
on any DLTtape IV cartridge using any DLT 4000, DLT1, DLT 7000,
or DLT 8000 drive can be read on a Super DLTtape drive.That
includes the majority of all the DLTtape drives ever built,and a very
high percentage of the 55 million DLTtape cartr idges ever built.
Next,we’ll take a closer look at the features that make DLTtape
technology the most reliable on the market today.
Tape direction when
in this orientation
Tape direction when
in this orientation
Figure 4-7 The Super DLTtape Backward Read Compatible Head
Assembly tilts to read DLTtape IV cartridges recorded on DLT 7000 and
DLT 8000 drives, which use Symmetric Phase Recording (SPR).
Reliability: The Heart
of the DLTtape System
QUANTUM DLTtape HANDBOOK
5
5.1
There is nothing more frustrating (or costly) than attempting to
restore a file or directory, only to discover it can’t be done because
of errors or worn out tape.An inexpensive tape drive suddenly loses
its appeal when a project manager is upset about a corrupted file
that can’t be restored.It doesn’t matter who deleted the original
version; it’s the IS manager’s fault. Suddenly,that too-good-to-betrue low cost tape drive looks more and more like a mistake.
You Count On Tape Backup
Reliability should be one of the main criteria you use to evaluate
tape backup systems.You need to match your organization’s backup needs to the expected reliability of your tape backup system.In
standalone workstation backup or other light-duty applications, a
low-end tape system such as QIC or DAT may make perfect sense.
This is especially true when you know you’ll use a tape just a few
times and archive it.
When it comes to network, enterprise and other mission-critical
backup situations, you can’t afford to cut corners.With data storage capacity at mid-to large-scale companies doubling every 12 to
18 months, you need a fast, reliable tape backup system that will
match your needs now and in the future. The DLTtape system was
specifically designed for today’s demanding mission-critical back-
RELIABILITY: THE HEART OF THE DLTtape SYSTEM5.2
up applications. In this chapter, we will take a look at the DLTtape
system features that make it the most reliable mid-range backup
system on the market today.
Unlike drives based on consumer video or audio recording technology,such as 8mm and DAT, DLTtape systems were designed
from the start for intensive data storage use in mid-range and high
end environments.DLTtape drive components and media work in
harmony to provide the fastest,most reliable, highest capacity tape
drives in the industry.
The following paragraphs outline the characteristics that give the
DLTtape system the reliability edge over all mid-range competitors.
Head Guide Assembly
DLTtape system reliability begins with a solid foundation: the head
guide assembly (HGA; see Figure 5-1). The patented DLTtape head
guide is a boomerang-shaped aluminum plate. In the DLT 4000,
DLT 7000, and DLT 8000 dr ives, it has six large bearing-mounted
rollers.These rollers are free-wheeling guides,with the last roller
acting as both a guide and a digital tachometer. The tachometer
controls the system’s two drive motors to regulate tape position,
speed and tension. The Super DLTtape drives have four rollers
(see Figure 5-2).
The DLTtape head guide provides a rock solid path for the DLTtape
media to follow.The precise head/tape alignment achieved at the
factory is maintained by the HGA. Other tape dr ives, particular ly
helical scan systems like the 8mm drive,have a much longer and
more complex tape path than the DLTtape system.A helical scan
system must pull its tape out of the cartridge and near ly all the way
around a cylindrical head. In addition, the tape path rollers used on
helical scan systems are small and result in acute tape wrap angles
QUANTUM DLTtape HANDBOOK 5.3
Figure 5-1 Patented Head Guide Assembly (HGA) used in the
DLT 4000, DLT 7000, and DLT 8000 drives provides a rock solid tape
path for industry-leading reliability and accuracy.
Drive
Leader
Head
Take-up
Reel
Tach
Assembly
Figure 5-2 The Super DLTtape Head Guide Assembly is a refined
version of the DLTtape Head Guide Assembly. It incorporates only four
rollers, further reducing contact and tape wear.
Head
Head Guide Rollers
Drive
Leader
Take-up
Reel
that stress the tape. DLTtape rollers are large and are arranged in a
gentle arc along the HGA.This roller arrangement results in much
less wear than in helical scan system.
When a DLTtape cartridge is inserted into the drive, it is automatically locked into position.A patented buckling mechanism pulls the
DLTtape media from its cartridge. Unlike 8mm and other cartridge
tape systems, DLTtape cart ridges have a supply reel, but no take-up
reel.The tape is pulled along the tape path (see Figures 5-3 and 5-4)
to a take-up reel mounted permanently inside the drive.In this way,
no space is wasted inside the DLTtape cartridge, al lowing for more
tape per cartridge. This design means the DLTtape system lets you
store more data in less space than other tape systems.
Tape Handling
The half-inch DLTtape media passes across the drive’s wr ite/read/
write head under very low tension. The only time the head moves is
Figure 5-3 Tape Path through the DLTtape head guide assembly is
a gentle curve that reduces tape wear and ensures tracking accuracy.
RELIABILITY: THE HEART OF THE DLTtape SYSTEM5.4
QUANTUM DLTtape HANDBOOK 5.5
Figure 5-4 Super DLTtape System Tape Path is even simpler
than that of the DLTtape drive, requiring only four precision rollers
to guide the tape.
to step up and down from track to track or, in the case of the
DLT 7000 and DLT 8000 drives, to tilt forward and back. The dr ive’s
head is gently contoured to minimize tape deflection at the contact
point. Low tape tension, a non-rotating head, and special wearresistant tape coating give DLTtape drives industry-leading head
life. The drive head is the only contact point on the data side of the
tape. The four or six tape path rollers touch only the back of the
tape, so wear is kept to an absolute minimum.In helical scan systems,the tape is wrapped around a large head that is spinning (at
over 5,000 rpm in one 8mm system).This large area of contact and
high relative tape speed result in wear to both tape and head.
The DLTtape system’s tachometer-controlled drive motors act in
tandem like an electronic Push-Me-Pull-You. One motor pulls the
tape through the tape path while the opposing motor applies just
enough drag to maintain optimal tape tension.When the tape
reverses direction,the roles of the motors reverse, too. The
tachometer also helps the system keep track of how much tape is
wound onto each reel and adjusts the speed of the two motors
accordingly. Each time a car tr idge is loaded, the drive calculates
and sets the minimum tension required to achieve high-quality,
consistent read/write signals. This calibration system maintains
optimal-contact recording and helps extend the operational life of
the drive.
Self-Cleaning Head
Another important feature that helps extend tape life is the
DLTtape drive’s self-cleaning head design. The write/read/write
elements on the head are aligned vertically on three tiny islands.
This reduces the point of contact with the tape recording surface
to a bare minimum.Along w ith the wr ite/read/write islands, two
additional islands are included (see Figure 5-5).These extra two
RELIABILITY: THE HEART OF THE DLTtape SYSTEM5.6
Outriggers
Read Heads
Write Heads Write Heads
Figure 5-5 Self-Cleaning Contoured Head on DLTtape
drives includes two fixed "outriggers" that wipe any debris from
tape, reducing head wear (top view of head).
Tape
QUANTUM DLTtape HANDBOOK 5.7
outrigger islands help wipe contaminants such as dust from the
tape as it passes. Like tiny stationary squeegees, these non-energized islands continuously clean the DLTtape media, ensuring
proper tape/head contact,and data integrity.
A low-stress tape path,contoured head,and self-cleaning desig n
team up to provide up to 1,000,000 tape passes.All DLTtape cartridges provide a shelf life of up to 30 years with just a five percent
loss in magnetic strength.
Error Detection
One quarter of the data on a DLTtape cart r idge is dedicated to error
detection and correction.An application-specific integ r ated circuit
(ASIC) chip containing a custom Reed-Solomon error-correction
code (ECC) maintains unfailing data security.For every 64Kby tes of
user data, there are 16Kbytes of ECC added. For every 4Kbytes of
user data, a 64-bit cyclic redundancy code (CRC) and a 16-bit errordetection code (EDC) are also added.In addition, each user record is
tagged with an overlapping 16-bit CRC.To top it off,all DLTtape
drives perform a read after each write command,and will automatically re-record data on a parallel channel.
This Parallel Channel Architecture (PCA) maximizes rewrite efficiency. Even with one or more channels inoperative due to bad
blocks, four-channel DLT 7000 and DLT 8000 drives can continue
to write data on a parallel channel (see Figure 5-6). (The dualchannel DLT 4000 drive also uses the PCA block structure and can
continue operation even with one channel blocked.)
Thanks to multiple levels of error detection and correction,
DLTtape drives offer an exceptional level of data integrit y.It has
been calculated that DLTtape drives have an unrecoverable hard
error rate of one in 1017bits and one undetected soft error in 10
30
bits. That is a standard that no other tape drive comes close to.
RELIABILITY: THE HEART OF THE DLTtape SYSTEM5.8
Adaptive Cache Buffering
DLTtape drives feature adaptive cache buffering,which helps
reduce stops and starts,reducing drive wear and tear. Adaptive
techniques enable the DLTtape system to adjust block sizes to
match the host data rate.If compression is on,data is compacted
as it enters the cache buffer at a rate that matches as closely as possible the rate at which it is written to tape.While the total throughput rate is dependent on how fast the host can supply data to the
DLTtape drive, adaptive cache buffering helps keep the drive
streaming as much as possible,and reduces delays due to repositioning. In addition, par ity is maintained between the host system
and the DLTtape drive over the SCSI interface.
Duty Cycle
Most drive makers base their performance and reliability figures
on drive utilization (duty cycle) as low as 10 percent.That means
that in a 7x24 operation, other drive makers base reliability figures
on as little as 2.5 hours of use during every 24-hour per iod. At
Quantum, we calculate most reliability figures based on 100 per-
1597 11
12131062
3
48
Channel 1
Channel 2
Channel 3
Channel 4
12 15 ECC1
7111416
ECC2
ECC3
ECC4
ECC4
Direction of Tape Motion
Figure 5-6 Parallel Channel Architecture on all DLTtape
drives (DLT 8000 shown here) automatically transfers data from
bad blocks to parallel channels for "on the fly" data recovery.
QUANTUM DLTtape HANDBOOK
5.9
cent usage.In fact, even at 100 percent duty-cycle, DLTtape drives
are rated at up to 250,000 hours Mean Time Between Failures
(MTBF). Even when compared to a competing drive offering the
same MTBF, DLTtap e drives are the clear winners, because we have
calculated MTBF assuming 100 percent usage.In practice,few drives will actually be subjected to non-stop operation.But,it’s nice to
know you could run your DLTtape dr ive continuously if you needed to without worry of premature failure or data loss.
The reliability and industry-leading performance that characterize
the DLTtape system are the reasons why nearly every major tape
library manufacturer offers DLTtape system-based products. The
DLTtape system is perfect for heavy-duty-cycle applications like
hierarchical storage management (HSM), in which the system is
constantly moving data between main memory,disk, and tape,
depending on its current level of usage.
According to the president of one of the world’s largest library
makers,“In HSM applications, we have a highly intensive cartridge-swapping environment. DLTtape drives and cartridges are
made for this heavy-duty application. This performance combination makes DLTtape technology solutions ideal within an automated HSM system.”
Next,we’ll discuss in detail what DLTtape system specifications really
mean to you.
Demystifying Tape
Drive Specs
QUANTUM DLTtape HANDBOOK
6
6.1
Specifications can be stated in different formats, using different
terms, which may or may not mean the same thing.And sometimes two different vendors will use the same term,but will base
their use of the term on very different standards.
For example,identical MTBF (Mean Time Between Failures) figures can be based on very different assumptions for duty cycle or
operating conditions (temperature and humidity).While both figures are accurate,different assumptions would make them have
very different meanings in real life.
We intend this chapter to be a helpful guide to reading and understanding specs for tape drives in the price and performance category
of Quantum DLTtape systems.That includes a range of drives typically used for backup,archiving, and near on-line storage applications.
It is difficult to make an exact,apples-to-apples comparison of
competing tape drives.That’s because all manufacturers tend to
state specs in the way that puts them in the best light.And,some
products are different enough that you really can’t compare them
apples-to-apples.We will give you a more in-depth view of what
each spec really means, what points you should look for, and how
to judge what specs may be important for your application and
DEMYSTIFYING TAPE DRIVE SPECS6.2
which ones you can ignore.Figure 6-1 includes the most important specifications for the DLTtape drives.
Capacity and Data Compression
Some manufacturers specify capacity in native mode.Others list
capacity with an asterisk, and a foot note that says something like
“assumes 2:1 compression.”Sometimes you might see a figure
without an asterisk, but that figure could still very well assume
compression of three or four to one.
Compression is the result of apply ing a compression algorithm to
the data before it is written to the tape. For a lot of applications,
compression is standard operating procedure.However, compression is only relevant if you actually compress your data,which you
may or may not want to do. Big blocks of text can be squeezed down
Figure 6-1 DLTtape Drives are the performance and reliability targets for all
others on the market today. This chart shows some of the important specifications
for DLTtape drives.
Native Capacity 20GB 35GB 40GB 40GB 110GB
Compressed 40GB 70GB 80GB 80GB 220GB
Capacity (2:1)
Native 1.5MB/s 5MB/s 3MB/s 6MB/s 11MB/s
Transfer Rate
Compressed 3MB/s 10MB/s 6MB/s 12MB/s 22MB/s
Transfer Rate
Drive MTBF (hrs) at 200,000 200,000 200,000 250,000 250,000
100% Duty Cycle
Head Life (hrs) 10,000 30,000 30,000 50,000 50,000
Tape Life (yrs) 30 30 30 30 30
Media Passes 1 million 1 million 1 million 1 million 1 million
Uncorrected Bit 1 per 10
17
1 per 10
17
1 per 10171 per 10171 per 10
17
Error Rate
Warranty (yrs) 3 3 3 3 3
DLT
4000
DLT
7000
DLT1 DLT
8000
SDLT
220
QUANTUM DLTtape HANDBOOK 6.3
very effectively, as can big graphics files. Other material, like tables,
for example,doesn’t compress much at all.Files that have already
been compressed may even get bigger if you try to compress them.
The bottom line is that compression may or may not be relevant to
your application,depending on the kind of data you deal with. Just
make sure that you compare native-to-native,or compressed-toequally-compressed figures.And, if the manufacturer has not been
very clear that the figure you see is native mode,you probably
should assume that the figure is for compressed data.For DLTtape
systems, the stated capacity is in both native mode and in compressed mode, assuming 2:1 compression.
Performance and Compression
Performance (data transfer rate) is typically described in terms of
MB per second.You need to determine if the transfer r ate figure is
for native mode,or if it assumes 2:1 data compression,or higher
compression ratios.Be careful to distinguish between terms like
peak transfer rate and sustained transfer rate. Peak transfer or burst
rate usually refers to the maximum transfer rate of the bus. It has
less to do with the performance of the tape drive than with interoperability with other equipment you may have in your system.The
performance figure you should pay attention to is the sustained figure.For the DLTtape system, we list both figures, in native mode.
Another performance-related figure is average access time.That is
the average time it takes to locate a file that is halfway into the
tape. It assumes this is the first access requested from this specific
tape, so the drive is starting to seek the file from the beginning of
the tape. This is a very conservative approach. It is appropriate in
applications in which files being sought are truly randomly distributed across the tape.However, in many,if not most, applications,
the next file sought is near the previous file accessed, and actual
access time may be shorter.
Load Time
Load time is the time from the moment you insert a cartridge into
the drive,until the cartridge is ready to read or write the data.
When discussing the DLTtape system,competitors often make the
accurate statement that the load time spec for a DLTtape cartridge
is approximately one minute.While accurate,that statement is not
complete.Load time for a DLTtape cartridge is approximately one
minute,but only for the first time a blank cartridge is loaded. After
that, it usually takes 35 to 45 seconds for the tape to load.The difference is due to the fact that,on the first load, the drive runs calibration tests and writes initial calibration information on the tape.
On successive loads of the car tridge, the drive need only read the
previously-recorded calibration information.
Compression Algorithms
One last compression related issue:how is compression accomplished? In most cases, compression is done by the tape drive itself.
Several different compression technologies are used. Quantum
DLTtape systems use the LZ (Lempel Ziv) compression algorithm.
This algorithm has advantages over other algorithms,in terms of
effectiveness across most types of data. In our experience, we have
frequently achieved compression ratios of 4:1, and have had specific instances as high as 25:1. However, for the DLTtape system,
Quantum continues to be conservative and uses the industry standard 2:1 figure when using compression data figures.
Reliability/MTBF
If your tape drive is subject to heavy usage,running eig ht or ten
hours a day, or if it runs all night doing backups, then reliability is
important, and MTBF is one way to determine reliability.MTBF is
the most commonly used reliability spec.It specifies the most likely
interval of time that will go by before the unit will fail.With some
exceptions,this refers to a failure of any part of the unit, for any cause,
under normal usage.A figure of 10,000 hours means that the manufac-
DEMYSTIFYING TAPE DRIVE SPECS6.4
turer claims that,on average, this unit will run for 10,000 hours (or
about 416 days) before it will break down and stop working.The bottom line is this:the DLTtape system,with its patented head design,lowtension-tape contact,simple tape path, and stationery heads, has an
inherently more reliable design than that of competitive products.
Reliability and Environment
Another spec to look at when you compare reliability is environmental operating conditions.MTBF is calculated based on a formula that
takes into consideration multiple factors for all the parts of the product and statistically merges them.Heat is the single greatest enemy of
reliability.So one very simple way to increase calculated MTBF is to
narrow the temperature range across which the product is assumed to
be running. If you assume the unit will always operate in a 70°F room,
you get a lot better figure than if you say it might have to function in a
100°F room.Our MTBF calculations for the DLTtape drives are based
on a temperature range of 50°F to 104°F (10°C to 40°C),a wide range
that reflects the worst conditions the system is likely to encounter.
Head L i fe
The read/write heads are among the most wear-sensitive and
expensive parts of the tape drive. Obviously,they are an important
factor in overall unit reliability. Head life for DLTtape drives is also
calculated in a fashion similar to MTBF for overall drive reliability
(i.e.,under severe temperature and humidity conditions).The
numbers would be even more impressive if we calculated for a typical office environment.Because head life is a cr itical reliability
measure, we are extremely conservative in making our calculation.
Durability: Tape Passes
Media durability is measured in tape passes.How many times can the
tape be run through the unit before it wears out? The figure we use for
the Quantum DLTtape media is 1,000,000 passes. However, you should
not compare that figure directly against c ompetitive drives,which usu-
QUANTUM DLTtape HANDBOOK 6.5
ally use far lower figures.A DLTtape drive lays down data in a series of
parallel tracks that run the length of the tape.As a result,it takes multiple passes to read or write the same amount of data on DLTtape media
that should be read or written in a single pass on competitive drives.
In general,a four-channel DLT 8000 drive will need 52 passes to
cover 208 tracks.If you divide 1,000,000 passes by 52,you get a figure
of 19,230 head passes.Durability figures for some competitive units
are in the range of 1,500 passes.Which still makes the DLTtape system more than 10 times more durable,e ven after adjusting for the
difference in technology. (This is the worst case scenario for DLTtape
recording.In operation, it is unlikely to require 52 passes to retrieve
the requested data in a typical cartridge usage, as only a small par t in
the tape will be read in most cases.) Again,this big advantage is based
on the basic design of the drive: the tape goes over the heads with
minimal tension (see Figure 6-2),and the heads are stationar y while
reading and writing.Wear and tear on the tape is dramatically less
DEMYSTIFYING TAPE DRIVE SPECS6.6
Figure 6-2 A Gentle Tape Path in all DLTtape drives reduces
stress and wear resulting in industry-leading tape life of up to
1,000,000 passes.
than for a drive with rotating heads.DLTtape media is more durable
than other types of media by a very wide margin.
Data Integrity – Error Correction
The important figure in terms of data integrity is the uncorrected bit
error rate,sometimes referred to as the hard error rate.Uncorrected bit
error rate is the number of erroneous bits that cannot be corrected by
error correction algorithms.For DLTtape and Super DLTtape drives,
we have calculated an uncorrected bit error rate of one bit in 1017bits.
That is one error in 100 quadrillion bits, or one error in 12 quadrillion
bytes.How does that compare to other technologies? Most DAT drives,
for one example,quote a spec of one uncorrected error in 1015bits.10
15
is 100 times less than 1017.Therefore,you can expect 100 times more
errors on the DAT drive than on the DLTtape drive.
Modern high-density tape technologies, which record more data
on smaller segments of tape, have made error correction quite
complex.High-density tape drives have to recover a higher per-
QUANTUM DLTtape HANDBOOK 6.7
1 5 9 13
141062
3
48
Channel 1
Channel 2
Channel 3
Channel 4
12 16
71115
ECC1
ECC2
ECC3
ECC4
Direction of T ape Motion
PRE POSTCONTROL
USER
DATA
USER
DATA
USER
DATA
S
Y
N
C
C
R
C
C
R
C
E
D
C
C
R
C
I
N
D
E
X
1
I
N
D
E
X
2
I
N
D
E
X
3
Figure 6-3 A DLT 8000 20-block Data Entity is shown above. Each
entity contains 16 data blocks and 4 blocks of Error Correction Code, ensuring data integrity.
centage of recorded data,and in larger blocks (measured in number of consecutive bytes) to prevent data loss.
During write operations, the DLTtape drive assures that the data
written is correct by performing a read after write. If an error is
detected,the drive rewrites the data block (see Figure 6-3) further
down the tape until the read-after-write check validates that the
block is now correct.In addition, the drive records powerful ReedSolomon ECC blocks on tape.
During read operations, if an error occurs, DLTtape drives recover
the data using powerful ECC code.DLTtape drives can recover up
to four bad blocks of data within a 20-block entity.At a recording
density of 62.5Kbits per inch, four consecutive blocks translates to
two inches of DLTtape media. That means that, even if as much as
two consecutive inches of tape are damaged on a single track, a
DLTtape drive can recover the data.
Conclusion
Comparing the specifications for the DLTtape system to the specifications for other technologies reveals significant benefits in a number of areas,including overall capacity,capacity per cartridge, and
transfer rate. In other areas, primarily reliabilit y,a comparison of
specs shows that the underlying DLTtape technology results in an
order-of-magnitude advantage.Leadership in speed and capa cit y are
certainly important, but it is in the area of reliability that the specifications reveal the most dramatic differentials between the DLTtape
system and competitive products.
Next,we’ll take a look at DLTtape media and discover the benefits
of Quantum DLTtape car t ridges.
DEMYSTIFYING TAPE DRIVE SPECS6.8
DLTtape Media
QUANTUM DLTtape HANDBOOK
7
7.1
A DLTtape cartridge is 4.16 inches w ide, by 4.15 inches deep,by
1 inch high. It weighs between 7.7 and 7.85 ounces, depending on
specific model.A DLTtape cartr idge holds between 1,200 and 1,828
feet of half-inch wide metal particle recording tape. A specially
designed 18-inch leader is at the front end of the tape. The tape cartridge enclosure includes a drive gear that engages with the DLTtape
drive,and a panel that opens to provide access to the tape.
Six types of half-inch DLTtape cartridges are currently in production:
CleaningTape III, DLTtape III, DLTtape IIIXT,DLTtape IV, DLT1
CleaningTape, and Super DLTtape I. Different cartridges are designed
to work with different models of DLTtape drives.However,one of the
things that has made DLTtape technology so successful is the fact that,
when we introduce a new DLTtape drive,we don’t make old DLTtape
media obsolete.Old tapes still run on the new drives.They won’t run
as fast as the newest model cartridges designed specifically for the
new drives,but they will run just as fast as they did on older DLTtape
drives.A tape originally recorded on a DLT 2000XT drive will run on
a DLT 8000 drive just as fast as it did on the DLT 2000XT drive.Even
more important,millions of DLTtape IV cartridges sold in the past
few years can be read by Super DLTtape drives.
DLTtape MEDIA7.2
What Makes DLTtape Cartridges Better?
For many DLTtape system users,the biggest difference between the
DLTtape system and other tape systems has nothing to do with transfer speed and cartridge capacity.It has everything to do with confidence that the information they put on a DLTtape cartridge two
years ago is going to be accessible with DLTtape drives they might
buy two years from now.With other tape technologies,this level of
media compatibility across generations has not been the case.Figure
7-1 shows which models of DLTtape cartridges are compatible with
which models of DLTtape drives.
Tape Type
(recorded on
drive type)
DLTtape IIIXT
(recorded on
DLT 2000XT)
DLTtape IV
(recorded on
DLT 4000)
DLTtape IV
(recorded on
DLT 7000)
DLTtape IV
(recorded on
DLT1)
DLTtape IV
(recorded on
DLT 8000)
Super DLTtape I
(recorded on
SDLT 220P)
15GB
20GB
35GB
40GB
40GB
110GB
1.5MB/s
1.5MB/s
1.5MB/s
1.5MB/s
1.5MB/s
NA
Native
Capacity
Native
Transfer
Rate
(read
on DLT
4000)
Native
Transfer
Rate
(read
on DLT
7000)
Native
Transfer
Rate
(read
on DLT1)
Native
Transfer
Rate
(read
on DLT
8000)
Native
Transfer
Rate
(read
on SDLT
220)
1.5MB/s
1.5MB/s
5MB/s
NA
5MB/s
NA
NA
1.5MB/s
NA
3MB/s
NA
NA
1.5MB/s
1.5MB/s
5MB/s
NA
6MB/s
NA
NA
1.5MB/s
3.5MB/s
3MB/s
4MB/s
11MB/s
NA=Tape format is not compatible with the tape drive.
Figure 7-1 Backward Compatibility Is Assured among the DLTtape system family.
Drives and matching DLTtape cartridges are shown here, along with transfer rate for each.
Access door Leader Supply reel
Write
Protect
switch
Tape
Drive access
QUANTUM DLTtape HANDBOOK 7.3
The one-reel design of the DLTtape cartridge offers two major benefits.First, the DLTtape cartridge has no wasted space. It is packed full
of tape,which means more capacity per cartridge. Second, the tape
path between the supply reel in the cartridge and the takeup reel in
the drive is very stable.Instead of tr aveling between two looselyanchored reels,as found in most dual-reel cassette systems, the
DLTtape media travels between the supply reel in the DLTtape cartridge and the firmly anchored internal take-up reel.(See Figure 7-2.)
Another feature very specific to the DLTtape cartridge is the tape
leader.Every DLTtape cartridge includes a specially designed tap e
leader at the front end of the tape. The leader on DLTtape III,
DLTtape IIIXT, and DLTtape IV cartridges includes a specially
designed loop.When the cartridge is inserted in the tape dr ive, a hook
at the end of the take-up leader securely mates with the tape leader
loop and gently pulls it through the HGA to the take-up reel.This
procedure is reversed when the cartridge is removed from the drive.
Figure 7-2 One-Reel Design of DLTtape Cartridge eliminates
the wasted space found in competing technologies and offers the
highest data density on the market.
On Super DLTtape I cartridges, a unique new buckling system
increases cartridge life and supports heavy-duty-cycle environments.
(See Figure 7-3.) A solid metal pin attached to the drive leader links
with molded clips that are permanently attached to the tape leader
inside the cartridge. The Positive Leader Link design makes the buckling of Super DLTtape I media a highly reliable mechanical process.In
addition to supporting Super DLTtape I cartridges, the buckling
mechanism supports existing DLTtape IV data cartr idges to ensure
complete backward-read compatibility.
This whole process by which the DLTtape system cartridge interacts
with the DLTtape drive is essential to the very high reliability and long
life of both the drive and the media.The combination of DLTtape cartridge and DLTtape drive results in a very stable, low-tension tape handling that results in longer life for both media and read-write heads.
Understanding The Differences
There are differences between DLTtape media,both minor and major.
For example,one of the subtle differences between DLTtape media is a
DLTtape MEDIA7.4
Super DLTtape
Drive Leader
DLTtape IV
Tape Cartridge
Leader
Super DLTtape I
Tape Cartridge
Leader
Figure 7-3 The Super DLTtape Positive Leader Link supports linking of
both DLTtape IV and Super DLTtape I cartridges.
difference in the position of the BOT (beginning of tape) hole (see
Figure 7-4).The BOT hole is a small hole in the tape that tells the drive
that the leader has passed the read/write heads and it’s now safe to start
recording.The distance from the beginning of the leader to the BOT
hole tells the tape drive what type of cartridge is loaded,the maximum
native capacity, and the length of the tape in feet.
Another small difference is that DLTtape cartridges come in four
different colors.The casing for DLTtape III cartridges is dark gray,
DLTtape IIIXT cartridges are white, DLTtape IV cartr idges are black,
and the CleaningTape III cartridge is cream colored. Super DLTtape I
cartridges are black, and have a distinctive textured finish,(See Figure
7-5.) These differences make it easy for users to differentiate between
tapes,especially in a situation where there are several different models of DLTtape drives working.
A major difference among the types of DLTtape media is capacit y.
The DLTtape III cartridge has a native capacity of 10GB, the
QUANTUM DLTtape HANDBOOK 7.5
Leader Splice
Scratch
Area
Calibration
Area
Directory
Area
DATA
SCRATCH AREA
■ Set Write Currents
■ Determine optimal tape
Tension
■ Individually adjust Write
Current for each write gap
CALIBRATION AREA
■ Position head in vertical
■ Determine optimal azimuth
position (DLT 7000)
■ Line up data tracks with cal
tracks for Interchange
■ Density Detection
DIRECTORY AREA
■ Used for Fast Search
BOT HOLE
■ Physical Beginning of Tape
EOT HOLE
■ Physical End of Tape
Figure 7-4 DLTtape Media Format features areas for calibration,
directory, and holes to indicated beginning and end of tape. Position of
BOT hole helps drive identify cartridge type.
DLTtape IIIXT cartridge has a native capacity of 15GB, and the
DLTtape IV cartridge has a native capacity of 35 or 40GB.
Super DLTtape I cartridges have a capacity of 110GB.
What accounts for the difference in capacity between cartridges?
There are several factors.First and most obv ious is tape length. Both
DLTtape IIIXT cartridges and DLTtape IV cartridges have a longer
tape than the DLTtape III cartr idge – 1,828 feet versus 1,200 feet. As
a result of the length of tape, combined with its half-inch width, the
total tape area contained in a DLTtape IV cartridge is over 10,000
square inches.(See Figure 7-6.) That is significantly more tape area
than competitive technologies offer, creating far greater potential for
capacity growth.
DLTtape IV media has significantly different magnetic properties
that result in higher capacity.DLTtap e IV media is double-coated
tape with a significantly smaller coating par ticle size than earlier
DLTtape MEDIA7.6
Figure 7-5 DLTtape Cartridges Are Color Coded for easy identification.
DLTtape III
DLTtape IIIXT
DLTtape IV
Super DLTtape I
QUANTUM DLTtape HANDBOOK 7.7
DAT QIC-MC QIC-DC 8mm Half-inch DLTtape
0
2,000
4,000
6,000
8,000
10,000
DAT QIC-MC QIC-DC 8mm
Media Recording
Area (square inches)
Figure 7-6 Half-inch DLTtape Media leaves plenty of room for
capacity growth for future DLTtape drives. A single DLTtape cartridge has
a tape area of over 10,000 square inches.
tapes (see Figure 7-7). Smaller particle size translates into the ability
to pack more data tracks into the same half-inch wide tape. The
higher-capacity DLTtape IV media also has different magnetic properties. For example, its “coercivity” rating is 20 percent higher.
Coercivity is a measure of the strength of the magnetic field needed
to change the magnetic orientation of a bit on the tape. The higher
the coercivity, the more magnetic energy it takes to change orientation, and the less likely it is for a particle to be “flipped”accidentally.
Therefore,higher coercivity means you can pack more data tracks
into the same space,and thus gain more capacity.
Super DLTtape I cartridges use state-of-the-art Advanced Metal
Powder (AMP) media. Designed to meet the needs of multiple
generations of Super DLTtape drives, AMP media ensures the
highest track density available today.AMP uses durable metal
powder technology for recording at very high densities, making
possible a dramatic increase in capacity.
Media Availability
Quantum Corporation sells all types of DLTtape and Super DLTtape I
cartridges. By setting up multiple channels of distribution for DLTtape
media,Quantum has sought to assure customers all over the world
that there will be an adequate supply of media available from multiple
sources,ensuring both availability and competitive pricing.At the
same time,customers can be assured of the qualit y of all DLTtape
media and DLTtape equivalent media,because it all meets Quantum’s
high quality controls.
Limited Warranty
All Quantum brand media carries a limited lifetime warranty that the
product is free from defects in material and manufacture.Only
Quantum-branded cartridges come with this warranty.Our warrant y
reflects our confidence in the extraordinary quality of DLTtape
DLTtape MEDIA7.8
DLTtape III
Magnetic Layer
(Metal Particle)
Magnetic Layer
(Metal Particle)
Non Magnetic Layer
(Titan Fine Particle)
Base Film
Base Film
Magnetic Layer
(Metal Powder)
Under Layer
Base Layer
Back Coat
with Servo Guides
DLTtape IV
Super
DLTtape I
Figure 7-7 DLTtape III, DLTtape IV and Super DLTtape I Media
Compared.
Finer magnetic particles used on DLTtape IV media allow for higher data density , while the Advanced Metal Powder Media in Super DLTtape I
media supports even higher density .
QUANTUM DLTtape HANDBOOK 7.9
media. That quality has been proven by over 55 million DLTtape
cartridges sold. These cartridges provide unsurpassed durability
and reliability. They are rated at one million tape passes, and have
an archival life expectancy of 30 years.
CompacTape
CompacTape was the name used for DLTtape medi a u n ti l 1996,
when the name was changed to “DLTtape.”The change was made
in order to make it easier for users to associate the correct media
with their DLTtape drives. DLTtap e cart ridges are clearly marked
with the DLTtape logo.
Next,we’ll take a look at one ofthe strongest areas of DLTtape
system growth – the automation mar ket.
Automation
QUANTUM DLTtape HANDBOOK
8
8.1
According to a report from the market research firm IDC, the overall market for tape libraries is growing at an annual rate of 25 percent,while the market for DLTtape system-based libraries is growing at a rate of 35 percent.Analysts estimate that 1999 shipments of
DLTtape-based tape autoloaders and libraries were 79,000 units,
and will grow to over 250,000 units by 2003.
The DLTtape System & Libraries: A Perfect Combination
At present,there are at least a dozen or more DLTtape systembased library manufacturers serving the mid-r ange market. As the
DLTtape syste m has become the leading standard for standalone
tape drive performance,capacity,and reliability, it makes sense that
tape library developers have very aggressively incorporated
DLTtape technology into their systems. (See Figure 8-1.)
The leading tape library manufacturers are also making commitments to incorporate Super DLTtape technology into their products. The introduction of Super DLTtape technology into advanced
tape automation solutions has had a dramatic impact on the tape
automation industry.The increased speed and capacity offered by
Super DLTtape technology is enabling library manufacturers to
offer significantly more capability at every point in the product
AUTOMATION8.2
spectrum, from compact desktop libraries to enterprise level systems.Super DLTtape technology also incorporates features
designed specifically to support librar y applications. Optional
library-ready models offer the high reliability demanded in continuous and random operations. Optional Memory Addressable
Cartridge (MAC) tracking systems let libraries and autoloaders
quickly review cartridge contents without loading them. Super
DLTtape's high data packing density means impor tant savings in
valuable data center floor space.
And, because both the physical and control interfaces are compatible with previous DLTtape drives, Super DLTtap e drives can be
integrated cost-effectively and seamlessly into existing automated
storage solutions.
Backup To The Future
There are many reasons for the rise in popularity of tape automation systems. One of the main challenges facing network managers
0
50,000
400,000
450,000
500,000
350,000
300,000
250,000
200,000
150,000
100,000
1998 1999 2000 2001 2002 2003 2004
DLTtape*
*
Including Benchmark’s DLT1 tape drive and
future generations of compatible DLTtape drives.
4 mm
LTO Ultrium
8 mm
Half Inch
Source: IDC June 2000
Worldwide T ape Automation Units Shipped
Figure 8-1 The DLTtape System Is the Overwhelming Choice
among high-performance tape systems for automated libraries.
QUANTUM DLTtape HANDBOOK 8.3
is the need to gain control of their r apidly expanding information
storage resources.The world of the mainframe is probably gone
forever. We now live in a world of distributed computing
resources,heterogeneous system env ironments, p erv asive
Internet/Intranet influence,and sky’s-the-limit application size.
The growing demand for more storage capacity among UNIX and
PC LANs, coupled with shrinking backup windows, has led to a
strong move toward recentralization of network computing power.
One of the key ways data managers are meeting this challenge is
through the use of backup automation in the form of tape stackers, autoloaders, and libr ar ies. By creating a centralized network
backup system,using automated storage management,network
managers can eliminate many of the scenarios that keep them
awake nights.
Applications For Tape Automation
As with standalone tape drives, the market for tape automation
systems is predominantly focused on backup,archiving, and
restore,the bread-and-butter of tape storage. Until computers can
be built that eliminate human error, this will probably always be
the number one application for tape storage systems.
Hierarchical storage management (HSM) is picking up momentum among high-end installations. HSM systems are used to manage large, critical databases and near on-line storage, and are not
true backup systems. If it’s truly critical that an application or data
be kept a key stroke away,a larger disk drive is increasingly the
solution used most often.
Other applications for tape automation systems include: near online storage, archiving, data collection, remote vaulting, tape
arrays, and image and video storage and distr ibution.
Growth of SANs and NAS
One of the major factors in the continuing growth of the market
for DLTtape-technology-based automated libraries will be the
emergence of new storage models, including Storage Area
Networks (SANs) and Network Attached Storage (NAS). Both of
these storage concepts place increased emphasis on the need for
high-performance, high-capacit y backup and recovery capabilities.
Those capabilities are being delivered by DLTtape libraries. (See
Figure 8-2.)
A Storage Area Network is a specialized network that provides servers
with fast, reliable access to a large pool of storage resources.A SAN
typically includes storage management software, a network infrastructure of hubs, routers, and switches, and may include Fibre Channel
(FC) connectivity.A SAN also includes a large pool of disk storage,
often in RAID configurations,and most often a large-capacity tape
library (or libraries) for backup.Applications for SANs are typically
ones that require large or very large storage capacity.They can be conventional horizontal applications (backup and archiving),as well as
data intensive vertical applications (e-commerce,data mining,medical
imaging, video, and multi-media). DLTtape-based libraries provide the
critical advantages of high capacity and performance, as well as reliability and a high-level of automated operation,reducing the need for
management and operator intervention to virtually zero.
Network Attached Storage (NAS) involves attaching storage resources
directly to the network,making them active nodes on the network,
easily available to servers on the network.The major benefits of the
NAS concept is that it is relatively simple to implement,because it
takes advantage of existing and proven network infrastructure.
Ty pically NAS is used in file-oriented applications, such as CAD,
graphic arts, and medical imaging . In these applications,NAS makes
high-volume storage available on the network to many users at low
AUTOMATION8.4
QUANTUM DLTtape HANDBOOK 8.5
Figure 8-2 Evolution of Storage Management
cost and with little management overhead.NAS, however,is not the
same as backup.In fact, by making it possible to easily expand storage,NAS creates the need for expanded backup capacity. This is
where DLTtape-based libraries fit in the NAS concept.In a typical
configuration,a DLTtape library is attached to a server designated as
the backup server.DLTtape libraries offer the speed, capacity,and
scalability to support the growing NAS capability,while delivering
reliable,automated backup.
Benefits of Tape Automation
The main reason for seeking a tape automation solution is probably because the previous backup system can no longer get the job
done in the available backup window. In addition, there are a
number of other benefits of tape automation.
Reduced human intervention. People make mistakes.Reducing
human intervention in the backup process invariably reduce errors
and downtime. In addition, it also reduces administrative overhead, provides hands-free file restoration,eliminates missed backups, and ensures data integrity.
User-friendly file management. Tape automation systems can provide users with self-serv ice file restoration. Time is saved and users
are empowered.
Cost-effective/fast ROI. Tape automation systems can often pay for
themselves in a matter of months through labor savings, reduced
downtime, and reduced media expenses.
Manages media rotation and storage.Your backup software and
tape automation system will let you set the media rotation strategy
that works best for you.
AUTOMATION8.6
Improved data security and availability. Backups become automatic, and backups are never missed. Data is secure and available
at a moment’s notice.
Seamless disaster recovery. With a two-drive system, a complete
copy of a full backup can be made at the same time the primary
copy is running. Disaster recovery becomes almost effortless. It is
still necessary to test disaster recovery procedures on a regular
basis, but you’ll know the data is secure.
Stacker, Autoloader,or Librar y?
The primary difference among tape automation systems is in the
way they handle data backup and access management.Stackers,
sometimes referred to as autoloaders,were the first tape automation products for small and mid-size IS operations. These systems
typically have one drive, and tapes are inserted and removed by the
system’s mechanical picker, sometimes called an elevator,in
sequential order. So,for instance, if a stacker is set up to perform a
full backup of a database, the system would begin with tape “0”
and continue inserting and removing tapes until the backup was
completed,or the supply of cartridges exhausted.
An autoloader, again, has one drive, but has the added capabilit y of
providing any tape in its magazine upon request.This abilit y to
randomly select tapes makes autoloaders appropriate for smallscale network backup and near on-line storage applications.
Libraries offer the same ty pe of functionalit y as autoloaders, but
are often equipped with multiple drives for handling large-scale
network backup,near on-line access,user-initiated file recovery,
and the ability to serve multiple users and multiple hosts simultaneously. On large libraries, multiple robotic mechanisms may also
be employed to improve system response time.
QUANTUM DLTtape HANDBOOK 8.7
How To Buy a Tape Automation System
What should you look for in a tape automation system? As in buying
a standalone tape drive,it’s best to begin w ith an evaluation of your
current situation and your future needs.For instance, how much data
do you need to back up? How fast is your data growing? How long is
your backup window? How much time do you and your staff spend
performing incremental and full back ups? How often will your
automation system be accessed? How critical is it that any new tape
system be compatible with your old system? Are you currently using
an enterprise backup software system,and does it support leading
tape automation systems? How much budget is available for a tape
automation solution? Be sure to factor in savings you may be able to
achieve in labor, media,and lost production time.
Inside Tape Libraries
Let’s take a moment here to look more closely at tape libraries.
What are you buying when you buy a tape automation system?
Every tape library comes equipped with certain basic elements.
(See Figure 8-3.) The next few pages describe these basic elements
briefly.
One or more tape drives. This is the heart of the system. The drive
capabilities and characteristics will determine, to a large extent, the
overall performance of the library,including capacity,throughput,
reliability, data compression, compatibility,and media consumption. Can you add additional drives (or higher performance drives)
at a later date to reduce user wait time,increase transfer rate, and
increase availability?
Multi-cartridge magazine or rack. Many library systems use cartridge magazines that can be loaded outside the librar y,then
plugged into the library when needed. This t y pe of system makes
life easier for the system operator. Some systems require cartridges
AUTOMATION8.8
to be loaded individually into storage slots inside the library.
Important Note:be wary of manufacturers’ total capacity claims.
Some library makers assume a 2:1 compression ratio in advertising
their total capacity. Compression is highly variable and data dependent and should not be used as a guide in evaluating library capability.It’s best to use total native (uncompressed) storage capacity in
comparing libraries. By multiplying the maximum number of tape
cartridges your library can hold by the total native capacity of each,
you can easily calculate the total native capacity of the librar y.
Robotic loader mechanism. Every library provides some type of
mechanical device to load and unload tape cartridges. This is the part
of the library that saves you time and allows you to perform unattended backups.The tape handling mechanism can also provide
users with self-service file recovery and near on-line storage access.
QUANTUM DLTtape HANDBOOK 8.9
DLTtape drives
Housing
Barcode
reader
Power
supply
Controller
card
Multi-cartridge
magazine
Robotic
cartridge
handler
DLTtape
cartridges
Figure 8-3 "Typical" DLTtape System-Based Library
Design
shows DLTtape drives, robotic cartridge handling system,
DLTtape cartridges, and controller mechanism.
Each library maker has their own tape handling mechanism.Some
of the different mechanisms you’ll find include robotic arms, elevators,and carousels.Some libr ar ies are equipped w ith multiple mechanisms.
Another feature to look for in larger libraries is a “mailbox.”This is a
slot or compartment at the front of the system that allows the operator to load one or more tapes without opening the main door and
interrupting library activit y.The key characteristics to look for in the
tape handling mechanism are proven performance over time (reliability), tape load/unload speed, and extra features like pass-through tape
handling.A pass-through capability allows multiple libraries to be
connected and share tape cartridges.This is especially important in
high availability applications in which a requested tape can be passed
between libraries to the next available drive. A proper drive-to-cartridge ratio can also provide high availability in most situations.
Library and loader controllers. Most libraries contain two physically-separate control devices to oversee over all library activity,as
well as loader movement.Both of these control devices are
equipped with microprocessors,local memory,and other electronics. Both devices communicate with librar y components and the
host computer via a SCSI interface.The loader controller follows
the directions of the library controller or the tape drive itself.
Pow er supply. Features you should look for in a power supply are
autoranging and growth capacity.If there’s a chance you may need
to ship your library to Europe,you may want to look for an autosensing power supply that automatically adjusts for U.S. or
European voltage (110 volts vs. 240 volts). If the library or lo ader
you’re considering is expandable, you should ask if the standard
power supply can handle additional drives,or does it have to be
replaced to accommodate them.
AUTOMATION8.10
QUANTUM DLTtape HANDBOOK 8.11
Protective housing. The higher the capacity of the library,the larger
the housing. From table top to room size,tape libraries come in every
shape and size.If you buy an expandable librar y system, you should
consider future space requirement when locating the library.S ome
libraries expand by stacking one on top of the other.Others are only
expandable from side to side.
Bar code reader. Most high-end libraries today come equipped with
bar code readers that help keep a running inventory of available cartridges and help speed tape selection. Among very large libraries,
you may want to compare tape inventory speed and selection time.
Start with DLTtap e Technology
A good place to start research on DLTtape libraries on the Internet,at
Quantum’s site at www.quantum.com or at www .DLTtape.com.
Every DLTtape library maker today has a Web site.The y offer at least
basic information on library features and options. In addition, ask
library makers for user references and make some calls.Ask associates
and friends if they use tape libraries. Many computer magazines
carry reviews and ev aluations of tape automation systems.
Focusing on DLTtape system-based automation makes sense for a
number of reasons. The market-leading benefits of the DLTtape
system have made it the favorite of library makers and users alike.
This popularity also extends to enterprise backup software.All of
the major software vendors support DLTtape standalone drives and
most of the DLTtape s ystem-based li brar ies on the market today.
DLTtape technology is proven, it has w ide ma rket acceptance, and
it has tremendous potential for even greater performance (see
Chapter 17 on the future of DLTtape technology). T he int roduction of Super DLTtape technology into librar y automation systems
has had a dramatic impact on the capabilities of librar y solutions
from the desktop to the enterprise.
AUTOMATION8.12
By starting with DLTtape system-based automation systems, you
know you’re getting rock-solid drives at the heart of the system,
drives that are renowned for reliable,error-free operation. Once
you’ve made the decision to select a DLTtape-based system,you
can focus on the automation vendor, robotics reliability, the
number of drives available,and the total capacity.With a DLTtape
system-based library,you’ll know that you’re getting industryleading data transfer speed, tape media capable of up to a million
passes, and head life of up to 50,000 hours.
It’s impor tant in comparing the advertised reliability of tape
automation systems to compare apples to apples. For instance,in
comparing MTBF rates, be sure to ask the maker what duty cycle
was used to calculate the rate.If you plan to use your library for
hierarchical storage management, near on-line storage or other
high usage applications, duty cycle should be an important factor
in your search for the ideal system.
Don’t forget to consider what your future may hold. Is the library system you’re considering expandable? Most high-end tape automation
systems can be expanded either by adding additional drives and cartridges within the existing housing, or by adding additional library
modules.These modules are usually a duplicate of w hat you have and
are linked by a common controller. Libr aries that link in this way
often have a pass-through feature that allows cartridges to be moved
to the next available drive,no matter where it may be located.
Software And Centralized Backup Management
As computing resources continue to become more decentralized,IS
managers are attempting to cope with this situation by centralizing
as many network resources as possible.Centralized data storage
QUANTUM DLTtape HANDBOOK 8.13
management and backup are becoming increasingly popular. Storage
Area Networks give users anywhere on the network access to a large,
centralized pool of storage resources sitting on their own high-speed
network – and backed up by DLTtape libraries.Tape automation systems and new versions of backup software make this a viable strategy.The use of high speed network backbones enable IS managers to
centralize file services without crippling network performance. With
the main file server in close proximity to the tape automation system,
a high speed link can be made that speeds backup even further.Some
organizations install dedicated backup servers to offload backup
overhead from the main file server. In a Network Attached Storage
(NAS) configuration,storage resources are attached as nodes on the
network,making available expanded storage resources with minimal
management overhead.
Most backup management software today supports library systems
and a centralized approach to data backup and information management. It’s important to find out which solutions will support
the tape library you’re considering. In addition, if your librar y wil l
be equipped with multiple drives, it’s important to discover up
front if your backup software supports simultaneous data transfers
to multiple drives.Not all do.
Next,we’ll take a look at the primary uses of the DLTtape system,
including backup and archiving.
Horizontal Applications
QUANTUM DLTtape HANDBOOK
9
9.1
No matter what business you’re in,or what industry-specific applications you may use,you almost certainly need data backup and
archiving. These are fundamental applications in the data storage
world,and this is where the DLTtape system is used most. In fact,
nearly 90 percent of all DLTtape systems sold are used for backup
and archiving. The remaining 10 percent are used in applications
such as Hierarchical Storage Management (HSM),near on-line
storage, tape RAIT (Redundant Array of Independent Tape drives),
library management systems, data interchange, and tape-as-disk
applications.
The widespread use of DLTtape technology for backup and archiving applications is easy to understand: DLTtape systems offer the
highest capacity,throughput, and cost effective reliability of any
tape systems on the market.If you are managing a computer network, data warehouse, or large Internet/Intranet application today,
no doubt you are experiencing tremendous growth in data storage
requirements.At the same time, your backup window may be
shrinking. In some 7x24 operations, there is no backup window –
backups must be accomplished during regular business hours.
Increasing data storage demands,coupled with shrinking backup
windows, have led users to embrace the advantages of DLTtape
HORIZONTAL APPLICATIONS9.2
technology.What follows is a look at the leading uses of the
DLTtape system and the data management issues you may
encounter when implementing them (see Figure 9-1).
Backup and Archiving
Basic backup and archiving are fundamental information management chores that every computer user should practice.From home
PCs to the largest computer systems and global networks,data
backup is your insurance policy against hardware failure, human
error, natural disasters, v iruses, and theft.
Overall, there is little difference between backup and archiving.
Backup is your day-to-day security,and may include incremental
updates and daily, weekly, or monthly full backups. Archiving is
simply a full (or image) backup that is then placed in some type of
Figure 9-1 Current DLTtape System Applications include
traditional applications such as backup and archiving, as well as
newer applications like HSM.
Other:
Data Collection
Remote Vaulting
Image/Video
Backup and Restore
Near On-line
Archiving
HSM
QUANTUM DLTtape HANDBOOK 9.3
protective spot for a period of time. Some companies,especially
those required by law to maintain historical records such as insurance companies and banks,archive data to special vaults or storage
sites specially designed to protect valuable records.
File-by-file vs. Image Backups
There are two basic forms of backup: file-by-file and image backup.File-by-file backups take much longer than image backups,
because the backup system must request each file from the operating system. File-by-file backups rarely achieve maximum tape drive
performance because the tape stops and starts frequently, preventing optimal streaming. System performance can usually be
improved by performing regular disk de-fragmentation.
Fragmented files and disks can take much longer to back up.
Image backups are like a snapshot of your disk at a moment in
time. Because data is sent to the tape in large, vir tually seamless
chunks,the tape drive is typically able to achieve optimal streaming and maximum performance. Image backups are important for
data restoration following a disaster or other catastrophic data loss,
when you want to restore everything on your system. Most imagebased backup systems also allow individual file restoration as well.
Real-time backup,a var iation on file-by-file backups, is available
with some data management software packages. These new software packages log changes to your data in real-time as they occur
on your network or file servers.This type of solution is a costeffective way to provide up-to-the-minute accuracy in data backup.
Real-time backup is increasing in popularity among 7x24 hour
operations where the backup window has been slammed shut.
The penalty for this ty pe of system is degr adation in server and network performance. However, as w ith any backup solution, the value
of the data must be weighed against the cost of the system required
to back it up.If the data is important, the cost in system performance and the cost of acquisition can be more than justified.
DLTtape systems are ideal for real-time backup because they minimize the drag on system performance caused by continuous
updates.
Near On-Line Storage
Near on-line storage is similar to hierarchical storage management.
It provides a large tape-based repository for information that is
important, but not impor tant enough to take up valuable hard
disk space. It is also good for a set of information that is too large
for the disk space available.Near on-line storage can be provided
by a single high capacity tape drive or by an autoloader or library.
Rather than simply backing up data to tape, and then removing the
tape and storing it in a closet, the information is left in the drive,
where it is available to users.
Depending on the type of near on-line storage system used, it may
take several minutes to locate a file. However, file location and
restoration can be accomplished unassisted,saving time and labor.
Applications for near on-line storage include marketing databases,
backing up multiple servers, report management, image storage,
video on demand, data warehousing and unattended backups.
The DLTtape system is ideal for near on-line storage applications
in which, unlike traditional backup systems, users repeatedly send
information to and from the drive.Inherent reliability, along w ith
market leading storage capacity and throughput, make DLTtape
systems the perfect choice for this application.
Tape-as-disk is a form of near on-line storage in which you use a
tape drive like you would a disk drive.The tape drive actually acts
as a second or third disk drive.You read and write to the tape drive
HORIZONTAL APPLICATIONS9.4
as if it were a disk. Only a handful of companies provide this type
of software application, and it’s typically used with desktop systems and not with servers or network access.DLTtape systems are
typically not used in this ty pe of application. Most tape-as-disk
systems use lower end,inexpensive tape drives.
Hierarchical Storage Management (HSM)
Hierarchical storage management is a multi-level approach to providing access to little-used,but critical information (see Figure
9-2).An important fact to note here is that HSM is not a backup
system in the true sense. In fact, HSM presents a new set of challenges to IS managers.
HSM systems migrate little-used files to and from your server’s
hard disk to lower cost storage media, usually tape. The data that is
migrated is still 100 percent accessible to the user, but recall speed
is slower. In many cases,HSM systems have solid state, hard disk or
QUANTUM DLTtape HANDBOOK 9.5
HSM
Front-end
hard disks
DLTtape
libraries
(deep storage)
Directories
Data
RAM
Internal
Disk
Figure 9-2 Hierarchical Storage Management (HSM) is a
structured way to migrate aging files to increasingly less expensive
storage media and still provide rapid access.
optical disk front ends that act as a high speed cache. The HSM
management software attempts to “anticipate”the file usage needs
of your users, based on criteria you set.
Files may be moved to progressively deeper storage based on the
date they were last used or the importance of the files. Newer or
more critical files may be kept on the HSM’s hard disk cache for
fast recall.As these files age,they may be moved off to storage in
the system’s tape library.
The challenge that HSM poses to IS managers is that HSM’s deep
storage tapes are generally not sent off site or archived in a traditional manner. HSM is active near-online storage and not a data
backup system.When data is moved further out in the hierarchy
by the HSM, a marker or pointer is left on the network server. This
pointer tells the HSM software where the file is located for
retrieval.
Your backup software must know what these pointers mean and,if
necessary,request the file from the HSM for inclusion in your full
backups. Not all backup management systems have this capability.
You should check with your HSM vendor to make sure the HSM
can be integrated with your backup management system.
With HSM systems,it’s important to consider the quality of the
deep storage component.Unlike normal backup systems,HSM tape
drive utilization will be on the order of 80 percent or more.The
drives and media used must be reliable and proven to w ithstand the
heavy use it will be subjected to.DLTtape drives have become the
standard for many HSM system vendors due to their inherent reliability,high densit y data storage, and high speed transfer rates.
HORIZONTAL APPLICATIONS9.6
Surprisingly,HSM systems are not proliferating as rapidly as originally expected. This is due in large part to the drop in price and
increased capacity of today’s disk drives.In addition, many library
and autoloader tape systems can perform many of the functions
that are typically associated with HSM systems. Libr aries and
autoloaders can provide vast amounts of near on-line storage,
unattended access for users,and fast backups. HSM systems vary
in features and capabilities; however, many allow for the hot swapping of components such as power supplies,drives,and cooling
fans without shutting the system down.
Virtual Tape
In many organizations,while applications are growing more data
intensive and more time critical,the time and resources available
for system management are diminishing. In situations in which
very large volumes of data must be backed up in very short windows of time, this situation has reached a crisis – even though
these organizations are already taking advantage of hig h speed tape
drives,probably running in multi-streaming mode. It is in these
circumstances that virtual tape is most likely to be an option.
Virtual tape is an emerging storage strategy that, like HSM, uses
multiple storage technologies to achieve performance goals.The
basic concept of v ir tual tape is that backups can be made dramatically faster by using high speed hard disk storage for a part of the
backup system. Most of the system's backup capacity is still in a
tape library or librar ies, but part of it is in the form of hard disk
drives,most likely a RAID unit.This disk capacity,however,presents itself to the system, not as a hard disk, but as a “virtual”tape
unit. This means the system can take advantage of the speed of the
hard disk,while still using all the existing backup software and
procedures;it is as if there is a super fast tape drive or library in
the system.While hard disk is a relatively small part of the total
QUANTUM DLTtape HANDBOOK 9.7
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