Results: 4 KB Random Performance
We turn to Iometer as our synthetic metric of choice for testing 4 KB random performance. Technically, "random" translates to a consecutive access that occurs more than one sector away. On a mechanical hard disk, this can lead to significant latencies that hammer performance. Spinning media simply handles sequential accesses much better than random ones, since the heads don't have to be physically repositioned. With SSDs, the random/sequential access distinction is much less relevant. Data is put wherever the controller wants it, so the idea that the operating system sees one piece of information next to another is mostly an illusion.
4 KB Random Reads
Testing the performance of SSDs often emphasizes 4 KB random reads, and for good reason. Most system accesses are both small and random. Moreover, read performance trumps the importance of writes when you're talking about typical client workloads.
We see the first hint that SanDisk's physically-similar drives are in fact like each other in other ways, too. All four SSDs trace identical lines though the chart, up until a queue depth of 32 where the Extreme IIs punch a bit higher and the X210s fall a bit lower.
4 KB Random Writes
Random write performance is also important. Early SSDs didn't do well in this discipline, seizing up even in light workloads. Newer models wield more than 100x the performance of drives from 2007, though we also recognize that there's a point of diminishing returns on the desktop.
In this benchmark, the delta between SanDisk's SSDs is significant. Our pair of X210s loses big to the incumbent Extreme IIs. What do we make of this? Not much, actually. To explain, let's flash back to a chart from the Extreme II review.
You see, using the 16 GB LBA space we test in, performance is tempered. This happens when we work with drives like Intel's SF-2281-based line-up, but in this case, SanDisk's nCache system is the most likely culprit.
So why isn't the X210's 50,000 IOPS such a big deal to us? SanDisk conservatively rates the X210 at just 60,000 4 KB write IOPS. Hitting 50,000 using a 16 GB LBA space turns out to be pretty good.
Here's a break-down of the maximum observed 4 KB sequential read and write performance with Iometer. The order the drives appear in our chart is determined by maximum combined read and write performance.
If you understood what was happening in the preceding paragraphs, it won't surprise you to see the X210s finishing just under the 120 GB Extreme II (not to mention a number of higher-profile aftermarket SSDs).