WSAT (Write Saturation) Test

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Summary:

WSAT is an easy-to-setup test that can be run with a variety of available test tools.  The test applies continuous RND 4KiB (random 4KiB) write stimulus to the drive after a Purge operation, and does not require preconditioning or steady state determination.  The basic objective of the test is to observe the time evolution of the drive’s performance as a function of time from a “factory fresh” (FOB) state.  It is a required test for PTS-E (PTS Enterprise), and can be very useful even for Client drives.  

Test Setup:

First PURGE the device, then apply continuous RND 4KiB write stimulus to the drive for 4X USER Capacity, or 24 hours, whichever event occurs first.  The test can optionally be lengthened to ensure steady state if desired.

Benefits of WSAT Test:

  1. Easy to Run:  Simply PURGE the device and apply stimulus.  No preconditioning or steady state requirement.  Steady state is determined in this case by inspection by observing the flat region near end of the test.
  2. Minimal Software Tool Requirement:  Many open-source software tools are available that can perform this test as the test requires only a single stimulus and no steady state determination.
  3. Verify Manufacturer Claims:  FOB (Fresh Out of Box) Peak RND 4KiB W Performance  allows comparison of SSD performance to the advertised "box-top" IOPS, often stated as "up to xxxx IOPS." 
  4. Observe Performance Evolution over Time and TGBW – This test shows performance evolution over Time and TGBW (Total Gibibytes Written) from a PURGED state.  On one chart, the test sponsor can observe the Peak IOPS, the duration of Peak FOB IOPS, the shape and length of the Transition Zone, and the Time, TGBW and IOPS values of WSAT Steady State.
  5. WSAT Steady State gives an indication of PTS IOPS Steady State - The steady state value obtained by inspection often gives a reasonably close estimate to the RND 4KiB results obtained via the PTS IOPS test which uses multi-Block Size, multi R/W mix preconditioning to Steady State.
  6. Compare & Correlate test environments.  Since WSAT can be easily run on different hardware / software test platforms, running WSAT tests allows the test sponsor to compare different test platforms and correlate test results.