Pre and Post Update Testing

We test to see the cause and effect.

Samsung launched their 840 Series SSDs back in May of 2013, which is over three years ago as of this writing. They were well-received as a budget unit but rapidly eclipsed by the follow-on release of the 840 EVO.

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A quick check of our test 840 revealed inconsistent read speeds.

We broke news of Samsung’s TLC SSDs being effected by a time-based degrading of read speeds in September of 2014, and since then we have seen nearly every affected product patched by Samsung, with one glaring exception – the original 840 SSD. While the 840 EVO was a TLC SSD with a built-in SLC static data cache, the preceding 840 was a pure TLC drive. With the focus being on the newer / more popular drives, I had done only spot-check testing of our base 840 sample here at the lab, but once I heard there was finally a patch for this unit, I set out to do some pre-update testing so that I could gauge any improvements to read speed from this update.

As a refresher, ‘stale’ data on an 840 EVO would see reduced read speeds over a period of months after those files were written to the drive. This issue was properly addressed in a firmware issued back in April of 2015, but there were continued grumbles from owners of other affected drives, namely the base model 840. With the Advanced Performance Optimization patch being issued so long after others have been patched, I’m left wondering why there was such a long delay on this one? Differences in the base-840’s demonstration of this issue revealed themselves in my pre-patch testing:

Pre-update testing

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Above is a sequential read-only pass repeated three times in rapid succession. Such a test performed on a pre-patched 840 EVO would have revealed repeatable slow results, but the situation was a bit different with the 840. With no writes taking place, read speeds actually self-improved, meaning that slowdowns seen by 840 owners would likely fix themselves the more the data was attempted to be read. The cause of this would be the 840 handling cell drift issues more gracefully than the (bugged) 840 EVO, which tends to lend some explanation to Samsung not being so quick to update this particular model. The above behavior would have also made it a bit harder for Samsung to replicate the issue, since running the test could impact the results of the subsequent test (that pesky Schrödinger's cat!).

Post-update testing

While our 840 sample returning to nearly full speed did put a damper on showing an instant increase after patching as we did with the 840 EVO update, our latency percentile results were still able to detect a noticeable additional bump in performance:

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…so here we see that while there were some IOs still taking longer to service, the number of them (and more importantly the total time taken by them) was reduced significantly just by updating to the new firmware. The same was reflected in IOPS averages scaling QD:

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Again, not dramatic due to the 840 speeding itself up during our pre-update testing, but still a measurable improvement. I suspect those patching lesser-used drives will see a more substantial speed gain after the update.

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I also noted increased read speeds across the whole drive in the very same test we ran before the update. The overall average increased by 56MB/s as compared with the pre-update test, again with no writing taking place.

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