HP 418371-B21 Performance factors for HP ProLiant Serial Attached Storage (SAS - Page 4
SAS use for enterprise systems, to 20 percent higher Input/output Operations Per Second IOPS
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Another important factor to HDD performance is seek time, described as the time from when a read or write action is initiated until the data transfer from or to the disk actually begins. The smaller platters of SFF SAS drives inherently yield lower seek times, an advantage in file servers with frequent random accesses. SAS use for enterprise systems This section describes SAS design features that affect the performance and operating efficiency of SAS HDDs for enterprise-class systems. For a general discussion of SAS technology, refer to the HP white paper "Serial Attached SCSI Technology" available at the following HP web page: http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00302340/c00302340.pdf Since RAID strategies and AFR numbers favor high-density systems, SFF SAS drives are an attractive solution for large enterprise systems. Compared to 3.5-inch large form factor (LFF) SAS drives, 2.5-inch SFF SAS drives have these advantages: • Lower AFR • 15 to 20 percent higher Input/output Operations Per Second (IOPS) • 30 percent smaller physical size • Up to half the power consumption Increasing HDD density in a RAID-based system invariably enhances the overall performance of the storage system. Increasing the drive density also expands the choice of RAID strategies as indicated in Table 2. Table 2. Comparison of drive support in two 1U HP ProLiant servers Server DL320 G5 DL360 G5 Drive type LFF SAS [1] or SATA SFF SAS or SATA # of drives 4 6 RAID support RAID 0, 1 [1] RAID 0, 1, 10, 5, 6 [2] NOTES: [1] Requires optional SAS controller [2] RAID 6 requires P400i with 512MB Battery Backed Write Cache option At the drive level, smaller/faster is usually better. SFF drives offer a spindle-per-U advantage that yields better performance in most systems. Traditionally, LFF drives have a cost-per-GB advantage over SFF types. For workstation and small-tomedium business customers, getting the most storage capacity for the money is a key factor in setting up a system. For the enterprise IT architect, however, the goal should be to get the most work (that is, more IOPS) out of the system, and this is best achieved with high density storage systems. 4