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The competition
To gauge the 750 Series' performance, we tested the 1.2TB add-in card against three PCIe SSDs: Samsung's XP941 256GB, Plextor's M6e, and Intel's own DC P3700 800GB. The Plextor and Samsung drives have similar per-gig pricing to the 750 Series, but they're confined to much smaller M.2 gumsticks. They also have slower Gen2 interfaces—two lanes for the M6e and four for the XP941—and AHCI underpinnings.

The DC P3700 (left), M6e (middle), and XP941 (right)

The P3700 is priced around $3/GB, so it's obviously in a different league. We've included it more for the sake of sibling rivalry than realistic competition. It will be interesting to see how the scaled-back consumer derivative compares.

Recent Serial ATA SSDs from Crucial, Intel, OCZ, and Samsung fill out the rest of the field. That group also includes a SATA 3Gbps drive from the old-timer's league: Intel's X25-M 160GB, which was released way back in 2009. The X25-M is marked with a darker shade of gray, while the PCIe SSDs are colored to set them apart from the SATA pack.

IOMeter — Sequential and random performance
IOMeter fuels much of our new storage suite, including our sequential and random I/O 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 750 Series lands in second place throughout our sequential tests, wedged between the faster P3700 and the slower XP941. Although it narrows the gap to the datacenter drive in the four-deep read test, it's mostly stuck at the mid-point between the two.

That said, the 750 Series hits well over 1200MB/s in the QD1 test, more than doubling the performance of the SATA drives. And it's even faster at QD4. Regardless of the queue depth, the XP941 is at least 200MB/s behind with reads and 500MB/s behind with writes.

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.

Although there's some intermingling between the PCIe and SATA SSDs, Intel's NVMe drives continue to occupy the top spots, with the 750 Series trailing the P3700 slightly. Both are consistently ahead of their PCIe competition, and their advantages are especially acute with writes at QD4.

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.