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Results: Latency And Performance Consistency

Samsung 850 Pro SSD Review: 3D Vertical NAND Hits Desktop Storage

Normally, I'd just use a garden variety workload generator for testing latency and performance consistency. It's simple enough that you could train a medium-smart kitten to do this stuff. But I like ULINK's platform; it gives me a common foundation for running benchmarks. That's not a big deal for some metrics, but it's more important for others. I have to use several different machines for testing with DriveMaster, due mostly to the length of time these workloads eat up. Two comparable systems deliver identical performance with DM2012.


ULINK's Latency test does things in a slightly different way than I've presented in the past. First, the drive is secure erased. Next, it is filled twice sequentially, then once with random writes. Immediately after, the latency test begins.

This script tests sequential one-sector accesses, sequentially testing 512 bytes. Do that 2 million times for reads and two million times more for writes, and presto. You get one result for reads and another for writes in the blink of an eye.

Samsung's hardware looks impressive. Not only do the 850 Pros serve up low latencies, but the 840 EVO and 840 Pro also hold their own. It takes the other contenders much longer to complete reads and writes under the same conditions, ending with Crucial's MX100. We'll do more of this testing on the drives waiting for reviews, but you can already see that going the budget route has negative implications.

Performance Consistency

This is another test I'd typically run differently. I don't even really like the phrase performance consistency. But I do like ULINK's PerfCon test. It offers six test cases: 4 KB read, 4 KB write, and 50% read/50% write in both aligned and unaligned boundaries. I won't bore you with the outcomes of all six test cases. Instead, I'll stick to the 50% read/50% write 4 KB aligned measurement.

The trick here is that after the same preconditioning used above, 1000 data points are generated one second apart. The 95.5th-percentile slowest result is divided by the average IOPS to yield one performance number reflecting consistency as a percentage. Absolute transactional performance is factored out of that number, so I display average, minimum, and maximum IOPS in a separate chart.

As you can see, the average, maximum, and minimum IOPS results are more even towards the top. In this 4 KB random workload split between reads and writes, steady state 4 KB write performance gets bolstered by reads. But it's more difficult for some drives to maintain when the workload is mixed.

Sure enough, Intel's SSD 730 ends on top, owing to its high average I/O performance. The Samsungs filter in behind. There's almost 2.5x as much difference between the slowest  and fastest averages. But how do the percentages play out?

The Vector exhibits some strange results, but 65% isn't bad for the MX100. Intel's SSD 730 attains an impressive 87%, and the 850 Pro contingent (led by the 256 GB capacity point) score a win. Each is above 91%, which is just great. Even without additional over-provisioning, the 850 Pros dominate in our look at consistency.

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