Samsung SM951 PCIe M.2 512GB SSD Review

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Mixed Workload and Steady State Testing

In the past, we could look at four-corner performance to get a good idea of how a product would act in the real world. That's no longer the case, though. Mixed-workload tests yield more useful info on what your SSD does while multitasking and running background software.

128K Sequential, 80% Read Mixed-Workload Performance

4KB Random, 80% Read Mixed-Workload Performance

The products we're testing today make this section fairly dry, but when you start looking at a larger sample size of SATA-based SSDs, the mixed-workload results get more interesting.

128KB Sequential Mixed-Workload Steady State Performance

In this test, we start out with the drives in steady state and then add sequential reads in 10% increments. Documents published by Intel suggest that consumer workloads should be measured with 80% reads and 20% writes. All drives give up performance when they're presented with mixed-data workloads, but we're looking for the product that suffers the least.

We brought in all of the PCIe-based M.2 drives we had on hand for this chart. Until the SM951, PCIe drives were actually slower than premium SATA-based products in our 80% read test. Many of the early controllers used modular designs with leftover vestiges of the SATA era. That would make them half-duplex and unable to process read and write commands at the same time. The SM951 is different; it performs exceptionally well under a mixed workload.

4KB Random Write Steady State Performance

We're looking for straight lines that show consistent performance, rather than large gaps between the highs and lows. SSDs that can serve up a stable experience are better for RAID arrays. Believe it or not, it's possible for two slower SSDs with consistent performance to outperform a pair of faster, more sporadic drives. Latency increases are compounded as the drive count in an array goes up, since one SSD has to wait on the other.

For PCIe-based M.2 products, we don't have to worry about RAID for boot arrays right now. The current rumor is that Intel will have a driver available around the release of Skylake for consumer PCIe RAID. 

Chris Ramseyer
Chris Ramseyer is a Contributing Editor for Tom's Hardware US. He tests and reviews consumer storage.
  • blackmagnum
    This is an awesome upgrade for some Macbook Air/Pro users, but just wait until Intel shows their product... and will there be any hardware compatibility issues with DIY upgrades?
  • Sakkura
    I'm disappointed the promised NVMe support did not materialize. But I guess Samsung is saving that for later retail products. Can't argue with the performance though, this is by far the fastest consumer SSD around.
  • Memory Ever
    May I know the model and nae of the PCIe adapter you used in the tests???
    No 1TB edition? Fail.
  • tom10167
    I wish they'd put an 840 or 850 pro in the comparison just to give us a better sense of scale. This drive is incredible, though, and $550 for a 512GB cutting edge drive is not terrible!
  • mapesdhs
    The Power Restricted Performance graph is stupid. Please stopping using
    graphs with origins that don't start at zero - the visual graphic impact is
    totally meaningless.


  • jeffunit
    You might want to fix the labels of your graphs. Latency in seconds? One chart shows a write speed of about 80 gigabytes per second.
  • liquidpower
    I also wished they put a 850 pro in the charts to see the jump from the fastest sata to the PCIe-based M.2
  • maestro0428
    You can purchase these at in the Enterprise SSD section. I want one!
  • generalsheep
    Is this little bastard bootable,so i can use it as my maindrive?