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Sustained and scaling I/O rates
Our sustained IOMeter test hammers drives with 4KB random writes for 30 minutes straight. It uses a queue depth of 32, a setting which should result in higher speeds that saturate each drive's overprovisioned area more quickly. This lengthy—and heavy—workload isn't indicative of typical PC use, but it provides a sense of how the drives react when they're pushed to the brink.

We're reporting IOps rather than response times for these tests. Click the buttons below the graph to switch between SSDs.

To show the data in a slightly different light, we've graphed the peak random-write rate and the average, steady-state speed over the last minute of the test.

The RD400's top random speed is rather lackluster, falling into the bottom half of our results. Even Crucial's budget BX100 500GB posts a higher peak rate. On the other hand, the RD400's steady-state rate is very good, almost doubling that of the 950 Pro. The 750 Series drive remains as untouchable as ever, doubling the speed of the RD400.

Our final IOMeter test examines performance scaling across a broad range of queue depths. We ramp all the way up to a queue depth of 128. Don't expect AHCI-based drives to scale past 32, though—that's the maximum depth of their native command queues.

For this test, we use a database access pattern comprising 66% reads and 33% writes, all of which are random. The test runs after 30 minutes of continuous random writes that put the drives in a simulated used state. Click the buttons below the graph to switch between the different drives. And note that the P3700 plot uses a much larger scale.

The RD400 scales well 'til QD8, after which its curve is more or less flat. That's a better showing than most SATA drives, but it leaves something to be desired when pitched against Intel's lineup. Just take a look at the next set of graphs.

The P3700 is miles ahead of the other drives, but we'd expect nothing less from this incredibly expensive datacenter drive. Still, even Intel's consumer 750 Series SSD exhibits much better scaling capabilities than the RD400. The Toshiba drive does manage to pull ahead of the 950 Pro, but not by a particularly significant margin.

Next, we dispense with IOMeter traces in favor of honest-to-goodness file I/O.