Performance factors for HP ProLiant Serial Attached Storage (SAS)

The AFR is less applicable for smaller systems but is meaningful for high-density infrastructures with

thousands or hundreds of thousands of drives. SAS drives, particularly small form factor (SFF) SAS

drives, typically have the lowest AFR.

Another important factor to HDD performance is seek time, or the time from the initiation of a read or

write action until the time a data transfer begins. The smaller platters of SFF SAS drives 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 Storage Technology” available at the following HP web page:

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01613420/c01613420.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 G6 DL380 G6

Drive type LFF SAS [1] or SATA SFF SAS or SATA

Number of drives 4 8

RAID support RAID 0, 1 [1] RAID 0, 1, 10, 5, 6, 50, 60 [2]

NOTES:

[1] Requires optional SAS controller

[2] RAID 6, 60, requires 256MB or 512MB with Battery Backed Write Cache and Smart Array Advanced Pack

(SAAP) License key options (standard on P812)

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., High density storage systems achieves this goal.

HDD performance comparisons

This section provides performance results of comparisons between HDD interface types, form factors,

and platter speeds. You should consider other factors that play a part in system performance when

evaluating systems, including the operating system, application environment, controller type, RAID

strategy, and general workload.