We benchmarked all the SSDs before we began our endurance experiment, and we've gathered more performance data after every 100TB of writes 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. What we're looking for here is how each SSD's benchmark scores change as the writes add up.
Apart from a few hiccups, all the SSDs performed consistently as the experiment progressed. That said, the Neutron GTX stumbled in the sequential read speed test near the end of its life. The 840 Pro's propensity to post slightly lower sequential write speeds increased as the experiment wore on, as well. Even though flash wear doesn't appear to have a clear impact on SSD performance, the data suggest that drives can become more prone to stumbling as writes accumulate.
Unlike our first batch of results, which was 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 result aren't useful for apples-to-apples comparisons. However, they do provide a long-term look at how each drive handles this particular write workload.
Samsung's 840 Series slowed a little at the beginning and more gradually at the end. The Intel 335 Series and the first HyperX also experienced small speed drops in their final hours, but those declines are nothing compared to the steep plunged suffered by the Neutron GTX. The fact that the Corsair SSD had been getting faster over time makes its final nosedive even more striking.
There's no evidence that the second HyperX so much as skipped a beat. The regular spikes for that drive (and some of the others) are an artifact of the secure erase we performed every 100TB.
Similar surges are evident on the 840 Pro's plot, where the peaks get shorter with additional writes. This drive exhibited a lot of run-to-run variance from the very beginning. The only break from that behavior is the band of narrower oscillation toward the end, which corresponds to the post-power-outage period leading up to 2.2PB. For the most part, at least, the 840 Pro was consistently inconsistent.