Samsung PM863 SATA 960GB Enterprise SSD Review

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.

 

Firstly, here are the results for the initial
Pre-Conditioning step (4K Random Writes) –

Myce/OakGate 4K Read and Write Latency Tests
Preconditioning –

 

Samsung PM863 SATA 960GB Enterprise SSD Review

Here we can
see that even after just under 7 hours the PM863 still hasn’t settled into a
steady state.  So, I decided to see what difference an initial pre-fill step,
of performing sequential writes would make –

Samsung PM863 SATA 960GB Enterprise SSD Review

In this preconditioning phase performing 4K Random Writes
has been preceded by performing 128K Sequential Writes to 200% of the PM863’s
total capacity.  I understand that the key difference this makes is to ensure
that all of the PM863’s LBA’s (Logical Block Addresses) have been written to as
well as every physical block.  You can see that following the pre-fill step the
drive has settled into a Steady State (of around 18,000 IOPS – bang on
Samsung’s specification) relatively quickly.  The difference must be down to
the way in which the PM863’s controller/firmware works and it is apparent that
the drive remains faster when all of the LBAs (Logical Block Addresses) have
not been written to.

For interest, this can be compared to the preconditioning
result that we observed recently for the Toshiba PX04SMB160, which did not have
a pre-fill step, and where there is a marked write cliff directly followed by
the immediate achievement of a Steady State once each physical block has been
written to –

 

Samsung PM863 SATA 960GB Enterprise SSD Review

The preconditioning phase with a pre-fill step was then used
to precede all of the following Myce/Oakgate Tests.

I must admit that I don’t know why drives should present
such a difference, depending on whether each LBA has been written to, but it is
clear why the SNIA tests specify a pre-fill step as a way to facilitate the
achievement of a Steady State.

 


4K Latency Read Test

Myce/OakGate 4K Read Latency Test

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see that the drive can no longer meet the increase in
IOPS demand beyond 93,000 IOPS.

 

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see that read latency remains below 160 microseconds
all the way up to its maximum IOPS level. This is an outstanding result. 

 

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see a clear Maximum Latency spike at the 32,000 IOPS
level.

Let’s have a close look at the distribution of the Latency
results at the 32,000 IOPS level –

Samsung PM863 SATA 960GB Enterprise SSD Review

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.

We can see that 99.9% of the Latency values are <= 190 Microseconds
and there are remarkably few outliers – the Quality of Service as measured in
this test is excellent.


4K Latency Write Test

Myce/OakGate 4K Write Latency Test

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see that in this test the drive continues to meet the
increase in demand up to a level of 19,000 IOPS.   

 

Samsung PM863 SATA 960GB Enterprise SSD Review

 

Here we can see that Average Write Latency stays below 50 microseconds
all the way up to a demand of 19,000 IOPS – an outstanding result.

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see that there are a few Maximum Latency peaks.

Now let’s have a look at the distribution of the Latency
Values at the 16,000 IOPS Mark (at one of the peaks) –

Samsung PM863 SATA 960GB Enterprise SSD Review

We can see that 99.9% of the Latency Values are <= 310 microseconds.
 There are only a relatively small number of outliers. This is an excellent
result.


 

Now let’s head to the next page, to look at the results
for the Myce/Oakgate Reads and Writes Tests…..