Plextor M6S And M6M SSD Review: Revving Another Marvell Engine

PCMark 8's Storage Consistency Test: New For Tom's Hardware

Futuremark's PCMark 8 takes everything that was good about PCMark 7's storage testing and makes it better. The standard PCMark 8 storage components include real trace activity for 10 different activities. These recorded I/O segments include productivity, gaming, and photo/video manipulation, yielding individual sub-tests. At the end, each category is scored in seconds, a master throughput score is conferred (similar to the average data rate in our Tom's Hardware Storage Bench), and the benchmark generates a total score.

In preparation for a transition away from PCMark Vantage and PCMark 7, I started testing PCMark 8 with Plextor's M6e. You'll see it appear in an upcoming review. But for now, this is what that drive looks like under PCMark 8 normally:

Although this is illuminating, the newest version of PCMark 8 Professional includes extended storage tests that let us dig deeper into SSD performance.

In truth, on a new or lightly-used drive, it's hard to distinguish one model from another. It takes tough workloads over long periods of time to expose the issues that might affect our recommendations. PCMark 8's storage consistency component is designed to hit SSDs with those workloads, getting consumer-oriented products dirty enough to sink the bad ones. 

Whether you run PCMark 8's normal or extended tests, those 10 traces form the backbone of this benchmark. As they're played against the drive under test, information is measured and recorded. The extended storage tests simply repeat the traces multiple times using varying conditioning procedures before each session.

First, the raw block device (there is no partition) is preconditioned twice by filling the entire accessible LBA space with 128 KB sequential writes. Once that is completed, the first degradation phase randomly writes blocks between 4 KB and 1 MB in size to random LBA spaces on the drive. Since the writes aren't 4 KB-aligned much of the time, the SSD's performance drops quickly. After all, non-4 KB-aligned accesses create overhead and generally increase write amplification significantly.

The first Degradation Phase begins with 10 minutes of those punishing random offset writes, after which each PCMark 8 activity trace is played against the SSD being tested. The successive degradation rounds are similar, except an additional five minutes are tacked onto each iteration. After eight repetitions, that write period expands to 45 minutes.

Next comes the Steady Phase. Each of five Steady Phases writes 45 minutes worth of random offset data prior to trace playback, pushing the drive even harder and making it more difficult to perform housekeeping duties. With fewer blocks available for writing, latency increases substantially.

Lastly, PCMark 8 moves into a Recovery Phase, which consists of five idle minutes before trace playback. Repeat that five times, and the test concludes.

This particular PCMark 8 test is brilliant in that it stresses SSDs methodically with preconditioning, followed by trace playback. You end up with a ton of data covering bandwidth, latency, and duration for all 10 traces and each of the 18 phases. But tracking that information lets us paint a picture of drive performance through each step of the benchmark. Every drive takes a beating during the Degradation and Steady Phases, but the Recovery Phase should push the most resilient drives to the forefront. SSDs that rely on garbage collection during write activity (and not background garbage collection) may not benefit much from this recovery time. 

Sounds like fun, right? With a bit of background out of the way, let's take our first look at the results.