OakGate Sustained Writes and Recovery Tests
Sustained Sequential Writes
This test starts with a purge (Secure Erase), so that the drive is in a FOB state, and then performs 128K Sequential Writes until twice the drive’s User Capacity has been written to.
Here is a graph showing the resulting Write Bandwidth over time –
Let’s zoom in on the first 120 seconds –
You can see that the Samsung 970 EVO holds a steady speed above 2,600 MB/s until 18 seconds has passed. This is clear evidence of the Samsung 970 EVO’s SLC Write Cache Technology being in play – as the drive is empty at the start of the test, the drive is able to write to around a capacity of 45GB before its SLC Write Cache is exhausted and the write speed crashes.
4K Random Writes, FOB to Degraded (Steady State) to Recovered
This test is designed to fully degrade the drive’s performance and then see how it recovers following a Trim and a period of Rest.
In this test I start with a purge of the drive to take it to a FOB state.
- FOB Performance – 4K Random Writes Bandwidth
I then test the FOB 4K Random Write Performance for 120 seconds at Queue Depths of 1 and 32, in an IO Range of 16GB, the result was as follows –
- Sequential Writes to two times User Capacity
I then performed 128K Sequential Writes to the drive for twice the drive’s user capacity (as in the previous Sequential Writes to Steady State test).
- 4K Random Writes for 1 Hour
This was immediately followed by performing 4K Random Writes to the drive for 1 hour. Here is a graph showing the resulting Bandwidth over Time –
You can see that the Random 4K Write performance eventually settles into a steady state around 140 MB/s.
- Fully Degraded, 4K Random Write ‘Steady State’ Performance
I then immediately test the 4K Random Write Performance (as we did in the initial FOB test), and the result was as follows –
You can see that performance has dropped significantly compared to the test performed in the FOB step. At this stage it is fair to say that the drive’s performance is fully degraded and in a Steady State. It’s as bad as it can get!
- Trim and Rest for 5m
I then liberally sent Sequential Trim commands to the drive for a minute (to ensure that the drive’s entire range of logical blocks (= User Capacity) was trimmed.
I then let the drive rest for 5 minutes before retesting 4K Random Write performance again. The result was –
- ‘Recovered’ 4K Random Write Performance after Trim and 5 minutes rest
You can see that performance has fully recovered to support the 20 second burst of 4K Random Writes at a Queue Depth of 1, but then the Samsung 970 EVO falls back to a somewhat degraded level of performance for the burst of writes performed at a Queue Depth of 32. I feel that this level of recovery is a bit disappointing.
For interest let’s have a closer look at the BW over Time, time graph for the 120 seconds of Random 4K, Queue Depth 32 writes –
I thought we would see a period where the Samsung 970 EVO performed at the FOB level followed by a period of significantly reduced performance (as we saw with the Adata Sx8200). What, we actually see is a reduced level of performance, which is largely steady throughout the period.
This can be compared to the 120 seconds of 4K, Queue Depth 32, writes in the FOB test at the start of the test –
You can see here that the peak speed was maintained through to the end of the 120 second period.
Now let’s head to the next page, to look at the Conclusions from this review…..