SNIA Write Saturation Test
This test performs random 4K writes.
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 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
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 –
Interestingly, a typical ‘write cliff’ isn’t apparent and a
gradual decline towards a steady state begins at round 46. It’s also apparent
that a steady state hasn’t been achieved at the time the test was halted.
We’ll take a closer look at this behaviour in the Myce/Oakgate 4K Latency Tests
later in this review.
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 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