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IOMeter — Sequential and random performance
IOMeter fuels much of our new storage suite, including our sequential and random tests. These tests are run across the full extent of the drive at two queue depths. The QD1 tests simulate a single thread, while the QD4 results emulate a more demanding desktop workload. (87% of the requests in our old DriveBench 2.0 trace of real-world desktop activity have a queue depth of four or less.) Clicking the buttons below the graphs switches between the different queue depths.

Our sequential tests use a relatively large 128KB block size. The results are color-coded to make the PCIe SSDs easier to spot, and the X25-M G2 is clad in a darker shade to set it apart from the other SATA drives.

In this first batch of tests, Intel's DC P3700 trounces the field regardless of the queue depth. Its lead is particularly pronounced in writes, where the drive nearly triples the sequential speeds posted by the Samsung XP941. The read results are much closer, but the P3700 still leads by around 400MB/s.

Samsung easily takes the race for second place. The XP941 outpaces the M6e by a wide margin in  sequential reads, and it's over 200MB/s ahead with writes. The M6e's write speed at QD1 is actually slower than for a handful of SATA SSDs.

The drives generally hit higher transfer rates at QD4, but that test isn't demanding enough for the P3700 to reach top speed. Intel recommends a queue depth of 128 for peak performance. That's a little outside the realm of what we'd consider typical for a consumer PC, though we have confirmed the drive reaches its potential at higher queue depths.

Before moving on, notice the X25-M languishing at the back of the pack. The drive barely breaks 100MB/s with writes, and its read speeds are about 50% slower than for the fastest Serial ATA drives. SATA SSDs have come a long way over the past six years.

Next, we'll turn our attention to performance with 4KB random I/O. We've reported average response times rather than raw throughput, which we think makes sense in the context of system responsiveness.

Once again, Intel's datacenter SSD takes the top spot with both queue depths. But its margins of victory are slim at best, and the PCIe drives don't have a definitive advantage over their SATA peers. The M6e and XP941 are right in the thick of things with the other SSDs.

Random read response times increase marginally with the queue depth. There are bigger slowdowns with random writes, but note the scale. Those differences still amount to less than a millisecond for everything but the X25-M.

The preceding tests are based on the median of three consecutive three-minute runs. SSDs typically deliver consistent sequential and random read performance over that period, but random write speeds worsen as the drive's overprovisioned area is consumed by incoming writes. We explore that decline on the next page.