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The war of attrition continues
We'll start with the Samsung 840 Pro, which has an unblemished record despite mounting reallocated sectors.

Flash failures started piling up after 600TB of writes. Apart from a few undulations, the retirement rate has been fairly consistent since.

The 840 Pro is now up to 5591 reallocated sectors, which translates to over 8GB of flash. That may sound like a lot, but it's only 3% of the drive's 256GB total. The SMART data indicates that we're only 61% into the used block reserve.

That reserve counter seems to be the best gauge for the 840 Pro's remaining life. The wear-leveling count is supposed to be related to drive health, but it expired 1.5PB ago.

Given what's supposedly still in the tank, 3PB doesn't seem impossible. The "good" health rating reported by Samsung's Magician software is encouraging, too, though it's hard to put a lot of faith in that assessment. Our failed 840 Series had the same health rating before its sudden demise. Unlike its fallen sibling, the 840 Pro has at least remained completely free of uncorrectable errors.

Before digging into the Kingston HyperX's vital signs, we should point out that this drive is running a different race than the 840 Pro and the other SSDs. The HyperX is based on a SandForce controller that compresses incoming writes to reduce flash wear (and to accelerate performance). Thanks this DuraWrite mojo, the HyperX has squeezed the experiment's 2PB of host writes into just 1.4PB of flash writes.

Now, that compression ratio is only applicable to our particular write workload. The surviving HyperX has been getting a stream of sequential data using the 46% incompressible "applications" setting in Anvil's Storage Utilities. To ensure an even playing field, completely incompressible data has been used for the other drives, including the first HyperX. The graph below illustrates the impact that difference has on the HyperX's compressed writes attribute, which tracks the true flash footprint of inbound data.

Write compression clearly isn't the only factor responsible for the remaining HyperX's survival. If that were the case, the drive would have quit around 1.1PB, when its flash writes matched those of its deceased twin. Digging deeper into the SMART data provides some additional insight on this candidate's exceptional endurance.

The lifetime attribute leveled out long ago, triggering a warning that drive is in a "pre-failure" state. Despite that ominous message, flash failures have been few and far between. Only 31 reallocated sectors have been reported through 2PB of writes, which translates to a mere 124 megabytes of failed flash. The death toll has risen slightly since we last checked in, but the total still represents no more than a blip.

Less than half of the reallocated sectors have been prompted by program or erase failures. The HyperX recovered gracefully from those hiccups, but it also logged two uncorrectable errors just before reaching 1PB. Uncorrectable errors can compromise data integrity, so we recommend taking SSDs out of service if any appear. While the HyperX remains in the experiment, a black mark taints its permanent record—and an asterisk denotes its compressible payload.

Caveats aside, there's no denying that the flash in this particular unit is incredibly robust. Since the HyperX is designed to keep writing data until its sector reserves are exhausted, this one may have a lot of life ahead. Then again, failure could be just around the corner. The other Kingston SSD went from 10 reallocated sectors to nearly 1000 over its last 128TB of writes.

With our health check-up complete, it's time to see if the aging survivors can keep up with their former, fresher selves. On to the benchmarks!