Sas Use For Enterprise Systems - HP 418371-B21 - Dual Port 72 GB Hard Drive Technology Brief

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
Drive type
# of drives
RAID support
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-to-
medium 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.
DL320 G5
LFF SAS [1] or SATA
4
RAID 0, 1 [1]
DL360 G5
SFF SAS or SATA
6
RAID 0, 1, 10, 5, 6 [2]
4