Much industry effort has been expended to define SSD Performance, and more specifically, the settling of Performance metrics over time and use. However, SSD marketing claims of “Up to XXX IOPS…” or “Sustained IOPS of XXX” continue to permeate the industry.
Marketing claims of “Up to XXX IOPS…” is synonymous with “Fresh-Out-of-Box” (or “FOB”) performance. This FOB metric has been clearly shown to be extremely transitory (out run in a matter of minutes or a few GB of writes). Further, FOB IOPS are a “peak” value which is not achieved after garbage collection and TRIM. At best, IOPS performance will achieve only some portion of the initial FOB IOPS measured immediately after a Purge of the SSD.
“Sustained IOPS of XXX” is a measure of IOPS performance after a pre determined type and amount of pre writes before IOPS measurements are taken. However, this “Sustained IOPS” value is highly dependent – and will vary – on the type and amount of pre writes (or preconditioning) to which the SSD is subjected.
Use of the “Steady State” IOPS value provides a more consistent and reliable measure of comparative IOPS performance. Using a pre defined and repeatable preconditioning ensures that the SSD IOPS measurements will be accurate, repeatable and reflective of IOPS performance as would be seen after normal use of the SSD.
One of the most reliable preconditioning methodologies is the Steady State preconditioning set forth in the SNIA Solid State Storage Performance Test Specification (“PTS”). This Steady State preconditioning methodology has been carefully developed and vetted by the SNIA Solid State Storage Technical Working Group – an association of over 54 leading SSD OEMs and Controller OEMs. The full PTS can be accessed in the following link.