We benchmarked all the SSDs before we began our endurance experiment, and we've gathered more performance data at every milestone since. It's important to note that these tests are far from exhaustive. Our in-depth SSD reviews are a much better resource for comparative performance data. Our goal here is to determine how each SSD's benchmark scores change as the writes add up.
Despite a few hiccups, our subjects have maintained largely consistent performance throughout the experiment. I can't explain the higher random read scores for the Kingston and Intel drives earlier on, but it's worth noting that those drives are all based on SandForce controller tech. They seem to be back to normal now.
Despite obvious signs of flash wear, the 840 Series has shown no signs of weakness in our performance tests. Its 840 Pro sibling stumbled during the last round, though. The drive's sequential write rate varied more than usual from one run to the next. We extended the test session from three to five runs, but the median speed was ultimately lower than at previous milestones.
The 840 Pro came close to its peak sequential write speed in a couple of test runs, so the recent variability may be a temporary anomaly. However, we have additional data suggesting that the 840 Pro's write speed may be slowing slightly.
Unlike our first batch of performance results, which were obtained on the same system after secure-erasing each drive, the next set comes from the endurance test itself. Anvil's utility lets us calculate the write speed of each loop that loads the drives with random data. This test runs simultaneously on six drives split between two separate systems (and between 3Gbps SATA ports for the HyperX drives and 6Gbps ones for the others), so the data isn't useful for apples-to-apples comparisons. However, it does provide a long-term look at how each drive handles this particular write workload.
From the beginning, the 840 Pro's average write speed in the endurance test has been the most erratic of the bunch. The other drives exhibit fluctuating speeds from one run to the next, too, but the amplitude of those oscillations has been substantially lower overall. Don't worry about the occasional performance spikes exhibited by some of the SSDs; those outliers crop up because we secure-erase the drives at every milestone.
Now, look at what happens to the yellow line after the last spike. Note that the highs and lows are slightly lower than they were earlier in the experiment. Hmmm.
Since the 840 Pro's write speeds in the endurance test have bounced around since we started the experiment, I'm hesitant to draw any firm conclusions about the recent reduction. The 840 Pro definitely exhibits inconsistency with this particular write workload, but we've seen it deliver strong all-around performance in a wide variety of benchmarks, so the variability isn't necessarily a concern on its own. We should have a better sense of what's going on with the 840 Pro as the experiment pushes past 600TB.
Before signing off until our next update, I need to take care of a little housekeeping. Between 300TB and 400TB of writes, the test rig hosting the Samsung drives and the compressible HyperX config crashed without warning. The event log reported an unexpected loss of connection to the system drive, and that disconnect seems to have caused the crash.
The system drive is a Corsair Force GT 60GB unit left over from an SSD performance scaling article we published nearly two years ago. It does little more than host the operating system for our test rigs, and it's only written a few terabytes in its lifetime. The drive's SMART attributes show neither reallocated sectors nor unrecoverable errors, so flash wear appears unrelated to the premature disconnect.
Around the time of the crash, everything about the system seemed fine. The SATA cable was attached, the PSU was pumping out the correct voltages, and the endurance test had been running without issue for days. SandForce-based SSDs of the Force GT's vintage do have somewhat of a reputation for being finicky, though. To avoid future problems, we've replaced the drive with an Intel 510 Series SSD. The machine hasn't suffered any disconnects since or crashes since, and testing is proceeding smoothly.
As I type this, our subjects are already well on their way to 600TB. We have another data retention test planned for that milestone, so stay tuned.