SNIA Write Saturation Test
The objective of this test is
to observe the time evolution of the drive’s performance, as a function of
time, from a ‘factory fresh’, ‘fresh out of the box’ (‘FOB’) state. When a
drive is in a FOB state (e.g. after it has been purged by, for example by a
SATA Secure Erase or SCSI Format), we can expect an initial period of time when
writes can easily be accommodated by clean/empty blocks, but once all of the clean
blocks have been written to once and the drive’s controller must first clean
blocks (with erase write operations) before it can write new data, then we can
expect a slow down. The slow-down is usually quite dramatic and is commonly
referred to as the ‘write cliff’.
The Write Saturation Test is
easy to run as it requires no steady state determination – it can be easily run
in freely available software, such as IOMeter.
Here are the results –
You can see here a steep fall followed by a gradual drop in
Write IOPS performance as the Toshiba THNSNJ960PCSZ reaches a Steady
State. The fall, that begins at around Round 47, is the ‘write cliff’.
Note that the test was halted, as specified in the SNIA SSS
PTS, when 4 x the User Capacity had been written to the drive. You can see that
the THNSNJ960PCSZ is settling towards a steady state at around the 25,000 IOPS
level, which is good for its target market segment.
You can also see that the latency graph line is a mirror
image of the IOPS graph line.
Now let’s head to the next page, to look at the SNIA