Hp COMPAQ PROLIANT 800, COMPAQ PROLIANT 6000, COMPAQ PROLIANT 1200, PROLIANT ML350 G2, COMPAQ PROLIANT 8500 technology brief, 2nd edition

Drive technology overview

technology brief, 2nd edition

Abstract.............................................................................................................................................. 2

Introduction......................................................................................................................................... 2

Categories of server disk drives............................................................................................................. 2

Characteristics of disk drives................................................................................................................. 3

Form factor...................................................................................................................................... 3

Capacity......................................................................................................................................... 4

Performance .................................................................................................................................... 4

Reliability........................................................................................................................................ 5

Drive qualification process.................................................................................................................... 6

Interconnect technology ........................................................................................................................ 7

Serial Attached SCSI ........................................................................................................................ 8

Serial ATA ...................................................................................................................................... 8

Excess bandwidth ............................................................................................................................ 8

Improved performance and reliability with RAID...................................................................................... 9

Advanced controllers ........................................................................................................................... 9

Emergence of solid state drives for servers .............................................................................................. 9

Performance of solid state drives...................................................................................................... 10

Reliability and operational environment of solid state drives ................................................................ 10

Conclusion........................................................................................................................................ 11

For more information.......................................................................................................................... 11

Call to action .................................................................................................................................... 11

Abstract

Disk drive capacity has increased at rates similar to those of microprocessor performance. New and
improved interconnect technologies allow the rapid transfer of large amounts of data to and from the
disk. New and more cost-effective applications are made possible by increased storage capacity and
reduced cost per bit. Through innovation and engineering expertise, HP develops industry-leading
disk technologies that optimize overall system capacity, performance, reliability, and value.

This paper reviews the classes of disk drives, the key factors determining capacity, performance and
reliability in single drives, the options available to connect the drives to the system, and the use of
multiple drives to further increase performance and reliability.

Introduction

Disk drives provide the primary mechanism for storing and retrieving permanent, or non-volatile, data
in almost all servers, desktop computers, and notebook computers. Disk drives are also increasingly
common in portable electronic devices such as music players and automobile navigation systems.

The key performance differences between main memory (semiconductor RAM) and primary storage
(typically, magnetic disk drives) are speed of access and capacity. Accessing primary storage is
typically approximately 1000 times slower than accessing main memory. Primary storage is typically
at least 100 times larger than main memory. Most engineering in disk drive and interconnect
technologies is driven by a desire to reduce this difference in access speed while simultaneously
increasing disk drive capacity and reliability. Innovative strategies in disk and disk controller design
continue to deliver dramatic increases in disk capacity, performance, and availability.

Flash memory technology, which has previously been used as a low-performance, lower capacity
storage medium in consumer devices, is being adapted for use as primary storage in computers. This
technology has the promise of delivering enterprise class storage with low latencies and performance
approaching that of RAM. The cost per bit for flash memory is between that of RAM and traditional
disk drives. Flash-based solid state drives that can meet both the performance and the heavy duty
cycle requirements of server storage are being introduced.

Categories of server disk drives

HP has refined and expanded its drive family to offer three distinct classes of server disk drives—
Entry, Midline, and Enterprise drives. Each drive category has a different set of performance,
reliability, and cost/capacity characteristics designed to meet the needs of different usage
environments. Meeting the requirements of each environment heavily influences both the design and
the component selections for the drives.

HP Entry drives have the lowest unit cost and provide a basic level of reliability and performance.
They are best suited for use in non-mission-critical environments where I/O workloads are 40 percent
or less. Typical intended applications for Entry drives are internal/archival storage or as boot disks
for entry-level servers.

HP Enterprise drives provide maximum reliability, highest performance, scalability, and error
management under the most demanding conditions. They are the only class of drives designed for use
at unconstrained I/O workloads and are intended for use in mission-critical applications such as large
databases, e-mail servers, and CRM.

HP Midline drives bridge the gap between Entry and Enterprise class by providing larger capacity
and greater reliability than Entry drives. HP Midline drives have improved resistance to rotational and
operational vibration, so they are better suited than Entry drives for use in multi-drive configurations.
For maximum flexibility, Midline drives are available with both Serial ATA (SATA) and Serial
Attached SCSI (SAS) interfaces.

HP Midline drives are designed for use in high-capacity applications such as external storage that
may require increased reliability. Like Entry drives, however, Midline drives are designed for use in
moderate workload environments and should not be considered for mission-critical applications.

Table 1 provides a side-by-side comparison of the three classes of HP server drives.

Table 1. Categories of HP server disk drives

Entry drives (ETY) Midline drives (MDL) Enterprise drives (ENT)

General
description

Usage
environments

Workload Designed for workloads

Reliability 2 times Entry drive

Interface SATA

Connectivity Single port Single port Dual port Single and dual port

RPM 5400 and 7200 7200 7200 10,000 and 15,000

Warranty 1 year 1 year 1 year 3 year

Performance and reliability
intended for entry-level
servers, lowest unit cost

Low I/O, non-mission
critical usages

- Boot disk

- Entry server storage

< 40%

1.5 and 3 Gb/s

High capacity, lowest
cost per gigabyte

- External storage

- Backups/archival

- Redundancy

Designed for workloads
< 40%,

reliability

SATA SAS
3 Gb/s 3 Gb/s

Maximum reliability and
performance using state of
the art design

- Mission critical

- High I/O

- Large database

- e-mail/messaging

Designed for unconstrained
workloads

3.5 times Entry drive
reliability

SAS
3 Gb

Characteristics of disk drives

This section identifies basic characteristics of industry standard disk drives and factors that affect
them.

Form factor

HP disk drives for servers are available in both 2.5-inch and 3.5-inch form factors. In general,

2.5-inch drives are used when power savings and space savings are considered important. The
smaller 2.5-inch drives can require as little as half the power and generate significantly less heat than

3.5-inch drives. On the other hand, 3.5-inch drives are better suited for uses that require large single
drive capacities and lower cost per gigabyte.

HP provides two lines of Universal Carrier for disk drives, one for 2.5-inch form factor drives and one
for 3.5-inch form factor drives. These carriers allow any hot-pluggable drive from a family to fit
mechanically and electrically with HP ProLiant servers or storage products. This mechanical
commonality extends to most SAS-based StorageWorks and HP Integrity server products as well. Thus,
mixed HP Enterprise solutions can be supported by a common family of hard drives.

Capacity

The capacity of a drive, measured in gigabytes, is set at manufacturing, and today’s drives are
capable of storing hundreds of gigabytes. The drive’s capacity is determined by the number of
platters it contains, the surface area of each platter, and the number of bits that can be stored per unit
area (called areal density). Areal density is determined by the number of tracks-per-inch of disk radius
multiplied by the number of bits--per-inch of track.

A common source of confusion regarding disk drive capacity is the definition of a gigabyte. In a disk
drive, a gigabyte is exactly 1,000,000,000 bytes, but operating systems often use the binary-based
approximation of 2
that a disk drive with 100 actual gigabytes of storage has only 93 gigabytes.

30

, or 1,073,741,824 bytes, per gigabyte. Thus, the operating system may report

Performance

Several factors determine the performance of a disk drive. They include the rotational speed of the
platters, seek performance, mechanical latency, read/write bandwidth, queuing strategies, and
interface technologies.

When preparing to read data from the disk, the drive head must move to the position above the
correct track and then wait for the target segment to pass under the head. This mechanical delay—the
time to move the head to the correct track and then wait for the target segment—is called the latency
or seek time.

Latency, which is fundamental to disk system performance, is measured in milliseconds (ms). Typical
values are 4 to 10 ms. A number of strategies have been developed to directly or indirectly avoid or
reduce this mechanical latency (Table 2). For example, doubling the rotation rate of the disk platter
can reduce the time spent waiting for the target segment to pass under the head.

Disk drive performance is usually characterized under one of two data transfer scenarios—continuous
data transfer rate of the media and random Input/Output operations per second (IOPs).

Continuous data transfer occurs when reading or writing relatively large blocks of data to sequential
disk sectors. It sets the upper boundary of performance for the drive. It should be noted, however, that
the maximum continuous data rate is valid only for the outermost tracks on the drive, and that this rate
can be up to 50 percent lower on the inner tracks.

Random access occurs when reading or writing relatively small blocks of data to sectors that may be
scattered across the disk. The speed of the actuator and the spindle determine performance in this
scenario and set the lower boundary of performance for the drive.

The performance of disk drives deployed in actual computing environments is heavily dependent on
the nature of the application; for example, whether it is dealing with large blocks of sequential data
(for example, video files) or small blocks of unrelated data (for example, customer records in an
e-commerce database). As a disk drive fills up, large blocks of data may have to be written to non­sequential segments or non-adjacent tracks. This scattering of data across the disk, called
fragmentation, can significantly degrade performance.