Quantum SDLT 220, SDLT 320 Handbook
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.
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