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 are put wherever the controller wants it, so the idea that the operating system sees one piece of information next to another is mostly just an illusion.
4 KB Random Read
At queue depths lower than eight, the Ultra Plus family takes charge and collectively runs at the top of the heap. It isn't until we hit the rarefied queue depths of 16 and 32 that higher-end desktop drives break away. More than 20,000 IOPS separate the fastest Ultra Plus from the leaders with 32 outstanding commands. It's far more important that SanDisk wins at lower queue depths, particularly in a client environment, though.
SanDisk's newer Extreme II enjoys a substantial advantage over the Ultra Plus line-up. But we'd expect that to be the case, since the Extreme II's controller has twice as many memory channels and a generational advantage. All things considered though, the difference is only significant once you have more than eight outstanding commands. We'd hardly call that a severe deficiency in a typical consumer environment. If you popped one of these drives into your mom's laptop, she's not going to complain about its performance.
All three capacity points hand in remarkably similar 4 KB random read numbers. There is some separation, but it's not very significant. In all actuality, we're not particularly surprised to see the smallest and largest models so close together as we step through the queue depths. It doesn't take much flash to achieve spectacular read performance, so you'd really only expect the big differences in write tests.
4 KB Random Write
SanDisk's drives don't do as well in random write tests. Collectively, all three show up as the slowest SSDs in this test. There is slight scaling above a queue depth of one, but they're all pretty much tapped out above two outstanding commands. The mainstream and performance drives in this 4 KB random write chart completely outpace the Ultra Pluses. Samsung's TLC-based 840 cannot stand up to the MLC-based 840 Pro, but it still falls in the same ballpark as every other non-Ultra Plus drive.
Random write performance is extremely important, no question about it. Early SSDs didn't do well in this metric at all, seizing up in even the most lightweight of workloads. Newer SSDs wield more than 100x the performance of drives from 2007, but there's a point of diminishing returns in client environments. When you swap a hard drive out for solid-state storage, your experience improves. Load times, boot times, and system responsiveness all get better. If you needed to, your SSD-equipped system could handle a lot more I/O than the spinning media you had in there before.
Neither the 128 nor the 256 GB Ultra Plus puts much distance on the 64 GB model. This could be a limitation of the four-channel controller. It's worth noting, however, that even the 64 GB drive is capable of twice the 4 KB random write IOPS of Intel's SSD 510. That's called progress, and we're all for it.