To compute for the dollar cost per IOPS, we add up the equipment
cost and divide the amount by the total IOPS generated. Equipment
includes the drives, enclosures, switches and cabinet. However,
for the purpose of this analysis, it is assumed that each setup
will utilize one switch. Therefore the cost of switches may not
be included in the computation since they would just cancel each
other out. List prices for the generic JBOD setup are based on web
prices as of June 29, 2005.
Analysis of Results
To compute for the $ cost per IOPS, the following formula will be
used using figures from Tables 4 and 5.
|
Total IOPS |
= $ / IOPS |
|
|
Total cost |
Table 6 figures reveal a significant difference in investment costs
when building a storage system for database/OLTP applications using
a generic JBOD versus an E-Disk®SAN. On a $/IOPS level, the rotational
HDD-based JBOD array costs 303.8 percent higher than the E-Disk®SAN,
thanks to the significantly higher I/O rating of the S2F-J solid state
disk subsystem which resulted in a lower number of drives required.
Another factor that drove down equipment cost is the smaller cabinet
space requirement of the S2F-J (24U) as opposed to the generic JBOD
(48U). In fact, the SSD-based subsystem can be easily integrated into
existing data centers since it is composed of only two 2U modules
as compared to the 20 modules required for the HDD-JBOD setup. Removing
the 24U cabinet (costing $4,298) in the S2F-J setup would drive down
$/IOPS even further.
Conclusion
Enterprises are looking for ways to generate more IOPS in the same
data center space, as well as cost-effective means of scaling their
storage performance requirements. The examples in the preceding section
prove that solid state flash disks are cost effective solutions for
performance hungry applications, not only in terms of $/IOPS in general,
but also for deferring costly server upgrades in I/O bound applications.
This article focuses mainly on the cost advantages of the SSD subsystem
in an equipment level. The gap between SSDs and HDDs widens further
when other factors such as power consumption of 220 rotational hard
drives versus 21 solid-state flash disks, storage space (and the burden
that these subsystems will impose on the data center's cooling system),
and better reliability (MTBF) are taken into consideration.
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