Results: Performance Consistency
Increasingly, we pay close attention to the performance consistency of enterprise-class SSDs. This is what separates a good drive from a great one when all of the corner case testing appears equal. Viewing the data with more granularity gives us insight on particular drive behaviors.
For the following tests, we subject Micron's M500DC and three comparison SSDs to 25 hours of continuous random 4 KB writes. We record IOPS every second, giving us 90,000 data points. We then zoom in to the last 60 minutes to more coherently visualize the results.
Overall, the M500DC performs well, even against more expensive drives. In fact, the M500DC substantially reduces the halo that we observed on Micron's P400m, though it can't quite match the tighter grouping delivered by SanDisk and Intel.
Looking at the distribution of data points reveals another interesting behavior.
Almost 96% of all data points are within 0.06 ms of each other, which is astounding. In comparison, SanDisk's Optimus Eco did not have any 0.06 ms-band that contained more than 58% of its data points. Really, our only complaint is the outliers around the 1.7 ms mark. Still though Micron's M500DC maintains its rated specification on nearly 98% of our measured data points. Even the outliers are at a respectable 18,000 IOPS.
Normally, we only post consistency data on a drive once it reaches steady-state. With the M500DC, getting to this point was more difficult than usual. The chart below shows a fresh M500DC with our random write workload applied.
It took nearly nine hours before the drive finally hit steady-state. We also found that if you aren't careful, the drive will trigger the TRIM command, and you get back to fresh out-of-box performance in a hurry. For what it's worth, only enterprise SSD reviewers get upset when a drive recovers its speed like this. And in case you're wondering, that stretch of data at the beginning lasts for almost an hour, with IOPS ranging from 66,000 to 78,000!
