Seagate 1200 400GB SAS Enterprise SSD Review

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) –

 

Seagate 1200 400GB SAS Enterprise SSD Review

A quick aside – for SAS drives we run the preconditioning step
at a queue depth of 128.  The following graph shows what happened with firmware
version 01, with which the drive was first supplied to Myce –

Preconditioning QD 128.png

You can see that the drive crashes to a low level of
performance after around 1300 seconds.  This crashed state would then persist
until the system was rebooted.  The problem went away once firmware version 04
had been applied to the drive.

 

 


4K Latency Read Test

Seagate 1200 400GB SAS Enterprise SSD Review

You can see that the drive can no longer meet the increase
in IOPS demand at 92,000 IOPS, which is a lot less than Seagate’s specification
of 110,000. Perhaps Seagate’s specification is for an earlier version of
firmware.

 


Seagate 1200 400GB SAS Enterprise SSD Review

You can see a
small and gradual increase in read latency up to the maximum IOPS mark. 

 


Seagate 1200 400GB SAS Enterprise SSD Review

You can see a
few max latency spikes.


Let’s have a
close look at the distribution of the Latency results at the 54,000 IOPS level
(at one of the spikes) –

Seagate 1200 400GB SAS 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.

You can see
that 99.9% of the Latency values are <= 820 Microseconds (0.82 Milliseconds)
and there are relatively few outliers, so the quality of service is good.

 


4K Latency Write Test

Seagate 1200 400GB SAS Enterprise SSD Review

You can see
that the Seagate 1200 begins to fail to meet the increase in demand at around
the 40,000 IOPS level (at the 40,000 level of demand the response is actually
below 39,000)


 

Seagate 1200 400GB SAS Enterprise SSD Review

Here we can
see that Average Write Latency stays below 50 microseconds until a demand of 35,000
IOPS.


Seagate 1200 400GB SAS Enterprise SSD Review

The maximum
write latency results are excellent, with no spikes until a demand of 38,000.


Now let’s
have a look at the distribution of the Latency Values at the 38,000 IOPS Mark –

Seagate 1200 400GB SAS Enterprise SSD Review

You can see
that 99.9% of the Latency Values are <= 2.72 milliseconds.  The quality of
service is excellent.


 

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