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)
General	Performance and reliability	High capacity, lowest
description	intended for entry-level	cost per gigabyte
	servers, lowest unit cost
Usage	Low I/O, non-mission	- External storage
environments	critical usages	- Backups/archival
	- Boot disk
		- Redundancy
	- Entry server storage
Workload	Designed for workloads	Designed for workloads
	< 40%	< 40%,
Reliability		2 times Entry drive
		reliability
Interface	SATA	SATA	SAS
	1.5 and 3 Gb/s	3 Gb/s	3 Gb/s
Connectivity	Single port	Single port	Dual port

Enterprise drives (ENT)

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

Single and dual port

RPM	5400 and 7200	7200	7200	10,000 and 15,000
Warranty	1 year	1 year	1 year	3 year

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 230, or 1,073,741,824 bytes, per gigabyte. Thus, the operating system may report that a disk drive with 100 actual gigabytes of storage has only 93 gigabytes.

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.