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Random Read/Write Speed

The four corners of SSD performance are as follows: random read, random write, sequential read and sequential write speed. Random accesses are generally small in size, while sequential accesses tend to be larger and thus we have the four Iometer tests we use in all of our reviews.

Our first test writes 4KB in a completely random pattern over an 8GB space of the drive to simulate the sort of random access that you'd see on an OS drive (even this is more stressful than a normal desktop user would see). I perform three concurrent IOs and run the test for 3 minutes. The results reported are in average MB/s over the entire time. We use both standard pseudo randomly generated data for each write as well as fully random data to show you both the maximum and minimum performance offered by SandForce based drives in these tests. The average performance of SF drives will likely be somewhere in between the two values for each drive you see in the graphs. For an understanding of why this matters, read our original SandForce article.

As we saw in our RevoDrive 3 X2 review, low queue depth random read performance doesn't really show much of an advantage on these multi-controller PCIe RAID SSDs. The Z-Drive R4 comes in a little faster than the RevoDrive 3 X2 but not by much at all. Even a single Vertex 3 does just fine here.

Random write performance tells a similar story, at such low queue depths most of the controllers aren't doing any work at all. Let's see what happens when we start ramping up queue depth however:

Surprisingly enough, even at a queue depth of 32 the Z-Drive R4 is no faster than the RevoDrive 3 X2. In fact, it's a bit slower (presumably due to the extra overhead of having to split the workload between 8 controllers vs just 4). In our RevoDrive review we ran a third random write test with two QD=32 threads in parallel, it's here that we can start to see a difference between these drives:

It's only at ultra high queue depths that the Z-Drive can begin to distance itself from the RevoDrive 3 X2. It looks like we may need some really stressful tests to tax this thing. The chart below represents the same data as above but in IOPS instead of MB/s:

271K IOPS...not bad.