Myce/OakGate 4K Read and Write Latency Tests
These tests steadily increase the random 4K IO demand in
terms of IOPS, and report the drive’s response in terms of Average IOPS, Average
Latency and Maximum Latency. It is designed to show a drive’s maximum IOPS
capability and report the all important Latency numbers for each level of IOPS
demanded. The Maximum latency numbers give us an insight into the occurrence
of Latency peaks that could cause an unexpected response from time to time.
Here are the results –
Firstly, here is a graph showing the result for the initial
Pre-Conditioning step (4K Random Writes) –
You can see what appears as a two step fall towards a steady
state. You can also see that there is a wide variation in performance around
4K Latency Read Test
You can see that the drive can no longer meet the increase
in IOPS demand at 88,000 IOPS, which exceeds Toshiba’s specification of 75,000.
You can see a small and gradual increase in read latency up
to the maximum IOPS mark. The Average Read Latency results are excellent.
You can see that the max latency spikes appear to occur at
regular intervals and are perhaps associated with a regular event occurring in
the controller’s housekeeping routines. Let’s have a closer look at what is
happening at one of these spikes.
Let’s have a close look at the distribution of the Latency
results at the 50,000 IOPS level (at one of the spikes) –
As this is the first time in this review, that we are
looking at a High Resolution Latency Histogram, here’s an explanation – The X
axis to the left is the count of the IOs in the observation period (in a Round)
that had a Latency of the value along the Y axis (please note that the X axis
is logarithmic to allow the low order counts of the huge number of IOs that
have been measured to be visible); the Y axis is the Latency value measured in
Microseconds; The X axis to the right is the % of the Total IOs observed that
have a Latency <= to a given Latency value; the rate of getting to 100% is
highlighted by the red graph line.
You can see that 99.9% of the Latency values are <= 170
Microseconds (0.17 Milliseconds) and there are relatively few outliers, so the
quality of service is excellent.
4K Latency Write Test
Perhaps we can see here why Toshiba only specifies a level
of 14,000 IOPS for 4K random writes as the THNSNJ960PCSZ starts to fall
slightly short of meeting an increase in demand at this stage. For example,
when the demand reaches 25,000 IOPS the response is actually falling short of
Here we can see that Average Write Latency stays below 200 microseconds
until a demand of 17,000 IOPS.
The maximum write latency results are a bit ‘spiky’ but this
Now let’s have a look at the distribution of the Latency
Values at the 20,000 IOPS Mark –
You can see that 99.9% of the Latency Values are <= 10.83
Now let’s head to the next page, to look at the results
for the Myce/Oakgate Reads and Writes Tests…..