Results: Performance Variation
Random Performance Over Time
My saturation test consists of writing to each drive for 12 hours using 4 KB blocks with 32 outstanding commands. But first I secure erase each drive. Then, I apply the write load, illustrating average IOPS for each minute (except for the last 20 minutes, where I zoom in and show you one-second average increments).
What we're doing here is taking a hard look at latency, quality of service, and consistency. Plextor continues to improve its products with an eye to the enterprise space. The M6e is decidedly enthusiast-oriented, but that doesn't mean some of the company's efforts don't trickle down into its behavior.
This chart comes from The SSD 730 Series Review: Intel Is Back With Its Own Controller. The 100% write (in pink), 50% write (in green), and 30% write (in blue) workloads are tightly grouped. There aren't any disturbing variations.
Now look at Adata's Premier Pro SP920 subjected to the same test:
The difference is significant. Each workload "band" is barely distinguishable, and there's a ton more variance from one second to the next, meaning a constant real-world application accesses I/O from the SSD inconsistently. If one operation depends on the previous one, there could be a comparatively long wait between them.
But the SP920 is representative of how most desktop SSDs behave. They typically aren't tasked with steady, demanding tasks. Conversely, in the enterprise space, predictably latency is key to building a reliable storage subsystem.
And that's why Plextor's result is so interesting. Have a look at this:
In the 12-hour scale, the company's M6e starts at 72,000 IOPS or so, which is typical after a few minutes. Then as the drive is filled, the PCIe-attached SSD starts putting up a fight, periodically reclaiming dirty, invalid blocks. Eventually, it gives up and ends up in a true steady state.
Break out a second-by-second graph of the three workloads shown above, and we see that the M6e looks a lot like Intel's SSD 730. With just 7% spare capacity to utilize, Plextor's M6e can't quite hang with the 730's significant over-provisioning, which means is doesn't achieve the same rarefied performance. But the variation is minimal, limited to a few percent.
If Intel is already celebrated for delivering I/O consistently, then Plextor deserves praise as well. By limiting the M6e's performance ceiling, it keeps its floor in check, too. That's not such an apparent advantage on the desktop. However, it's a good sign that an SSD is designed hold its ground under the most grueling storage workloads.