Abstract; Introduction; Hdd Controller Technologies - HP 418371-B21 - Dual Port 72 GB Hard Drive Technology Brief

Abstract

Enterprise-class hard disk drives (HDD) must meet the maximum reliability and scalable performance
goals of the 24/7 enterprise environment. Serial Attached SCSI (SAS) has become the defacto HDD
standard for mission-critical applications. This paper explains the emergence of SAS and the key
parameters of SAS drive technology. It also includes technical data and comparison information of
the latest small form factor SAS drives available from HP at time of publication.

Introduction

The mission-critical, 24/7 enterprise environment places stringent demands on storage technology.
Reliability and performance are of paramount importance. While server downtime can be costly, even
slow server performance can increase operating costs. Hard disk controllers, interfaces, and drives
have evolved to address the reliability and performance issues of the enterprise storage system.

HDD controller technologies

To enhance the operating efficiency of multiple drives, HDD controllers use logic-based solutions
including:
• Data buffering and read/write caching
• Queuing control and read/write reordering
• Error management and pre-failure warning
• Redundant Array of Independent Drives (RAID)
HDD controllers employ on-board data buffering and caching techniques to avoid the use of slower
system memory. Queuing techniques such as Tagged Command Queuing (TCQ) and Native
Command Queuing (NCQ) allow controllers and compatible HDDs to take advantage of the
read/write head position for more efficient drive operations. RAID is another logic-based solution that
places data in stripes across multiple drives to enhance reliability, performance, and data integrity. A
variety of RAID strategies 1 are in use:
• RAID 0 – Striping to two or more disks (no parity) for performance improvement (no redundancy)
• RAID 1 – Mirroring data on two disks (no parity) for redundancy, slight performance improvement
• RAID 0+1 – Mirroring and striping for redundancy and performance improvement
• RAID 1+0 (10) – Mirroring and striping for redundancy and performance improvement
• RAID 3 – Striping (byte level) with parity for improved performance and fault tolerance
• RAID 4 – Striping (block level) with parity for improved performance and fault tolerance
• RAID 5 – Striping with distributed parity for improved performance and fault tolerance
• RAID 6 – Striping with dual parity for improved performance and fault tolerance 2
The choice of RAID strategy depends on the desired balance of protection and performance, along
with the number of hard drives available.
1 For more information about disk drive technology and RAID refer to the HP technology brief titled "Disk Drive
Technology Overview" available at
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01071496/c01071496.pdf .
2 For more information about RAID 6 technology refer to the HP technology brief titled "RAID 6 with HP ADG
Technology" available at
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00386950/c00386950.pdf
2