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How to calculate the costs of solid state drives

John Scaramuzzo | Sept. 19, 2013
Many organisations are considering swapping out some of their HDD for SSD to increase I/O throughput and power density. But how do you compare cost vs. performance to determine the best technology mix for specific application environments?

Drive IOPS


" IOPS: expected I/O operations per second

" %R: percentage of IOPS that are reads

" %W: percentage of IOPS that are writes

" WP: RAID Write Penalty (RAID 1 or RAID 10 = 2)

" 2,000 users x 3 IOPS per user = 6,000 IOPS

The number of 15K 146GB SAS HDDs required is:

[(6,000 x 0.65) + 2(6,000 x 0.35)]/479.7 = 17 (or 18 HDDs for RAID 1 configuration)

The SNIA SSD TCO Calculator can determine and recommend the number of required SSDs based on the following four key inputs from the user:

" Minimum consumed HDD capacity

" IOPS for HDD (4Kbyte block size)

" IOPS for SSS (4Kbyte block size)

" Minimum RAID requirements

When using the above data, the SNIA SSS TCO Calculator recommends the user to replace the 18 HDDs with two SSDs in this Microsoft Exchange Email Server example.


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