HP 418371-B21 Performance factors for HP ProLiant Serial Attached Storage (SAS - Page 2

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 strategies1 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 tolerance2 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