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Samsung SM951-NVMe M.2 SSD Review

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Samsung’s new drive uses the NVMe protocol bringing various performance improvements. As such, looking at its potential performance, the new SM951-NVMe is quoted to reach sequential data read and write speeds up to 2,260MB/s and 1,600MB/s, respectively. These figures are slightly better than the PCIe 3.0 version, which touted a maximum of 2,150MB/s read and 1,500MB/s read for the 512GB model. Looking at its random read operations specifications, Samsung indicates that the SM951-NVMe can process 300,000 IOPS, which is more than twice the speed of the 130,000 IOPS rate of the PCIe version.

Samsung SM951-NVMe M.2 SSD Review

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Excellent drive and a nice review, as always. And some comments from my side:

- The previous SM951 is the AHCI version, not the PCIe version. Both of them use PCIe for the data transfer.

- "speeds that were by in far the fastest" -> "speeds that were by far the fastest" (I know it's somewhat common and I've already seen it in several SR reviews, but the "in" makes no sense there)

- You're comparing a 512 GB AHCI drive versus a 256 GB NVMe drive. That's OK since you're working with what you have. You also list the performance difference due to the smaller capacity in the drive specifications. Yet when you compare the 2 drives, you never mention that part of the performance difference is due to the NVMe driver having fewer NAND dies. Otherwise the AHCI version should never be faster and your results would actually look very strange. This in turn means a 512 GB NVMe drive would be even faster. From my point of view this is a basic analysis of your results, which should not be left up to each reader.

MrS

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The distinction was brought up around the SATA vs PCIe vs NVMe versions in laymen's terms. Got a lot of drives bunched into the M.2 category right now.

I think its more of a common Canadian term that one of our writers brings into reviews ;)

Its hard for us to comment around differences when comparing versions we don't have access to. Samsung lists the same spec for the 256 and 512GB NVMe versions, so we don't know if additional NAND die would make a difference. As we found in the traces, both the AHCI and NVMe models had roughly the same level of performance.

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Thanks for the answer, Kevin.

Regarding the 1st point: well, neither drive is SATA. As far as I understand one is PCIe AHCI and the other one is PCIe NVMe.

Regarding the capacity vs. performance: Samsung does quote a difference in sequential write performance, taken straight from your review:

  • 512GB - Up to 1,550MB/s
  • 256GB - Up to 1,260MB/s

and for the AHCI version, also taken straight from the SR review:

  • 512GB - Up to 1,500MB/s
  • 256GB - Up to 1,200MB/s

This makes it even more astonishing that the NVMe version can often keep up with or beat its AHCI cousin. I know it's not easy to comment on drive sizes you don't have in-house, but this doesn't mean you should ignore known differences either.

MrS

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SATA was in reference to the other M.2 SSDs on the charts. Point taken on the capacity/performance notes.. I'll push Samsung on sending a sample and it will bypass the issue once we have some hard numbers :)

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Nice article. It said an HP z620 was used to benchmark the SM951 NVMe. However, the z620 doesn't have a M.2 interface socket. Was a M.2 PCIe to PCIe 3.0 x4 adapter used to host the SM951? If so, which one? And which PCIe slot was used on the z620? Thanks.

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Hello,

What OS and drivers did you use to benchmark the 951 NVMe? I've just purchased on and I'm getting horrific write speeds. In every case between 2 and 10 times slower than the AHCI variant!

I am testing under Windows 8.1 x64 on an Asus Z97i-plus using a PCIe card to interface the 951 SSD,

Apparently it's a sample rather than a production unit but I'm seeing fantastic read speeds but horrific write speeds. In my case I'm using with an Asus Z97i-plus with the latest BIOS. The board identifies the 951 and allows me to install windows (8.1 all latest updates)... so far so good. Unfortunately when I run speed tests against the NVMe variant I get 10 times slower write speeds compared to the AHCI variant.
CrystalDiskMark: AHCI variant (connected to PCIe 3.0 bus)
Seq Q32T1 - 1172MB/s read | 1043MB/s write
4k Q32T1 - 398MB/s read | 289MB/s write
Seq - 1052MB/s read | 900MB/s write
4k - 35MB/s read | 128MB/s write
CrystalDiskMark: NVMe variant (connected to PCIe 3.0 bus)
Seq Q32T1 - 2264MB/s read | 501MB/s write
4k Q32T1 - 563 MB/s read | 21 MB/s write
Seq - 1299 MB/s read | 170 MB/s write
4k - 54 MB/s read | 0.98 MB/s write
Blindingly fast read but horrifically slow write speeds.
I've also tested using the Z97i-plus's M.2 slot. I see reduced read speeds due to the limited, 10Gbps, speed of the M.2 on this board but the same horrific write speeds.
Is there something that I might be doing wrong? Could this be a BIOS problem? A Windows NVMe driver problem?
Thanks
Chris
Edited by carukc

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We tested using Windows 8.1 (stock image from MSDN) and the drivers it includes. Where did you get the card? It sounds almost like it has some really bad NAND failure. NVMe should just work without intervention.

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The card came from a supplier here in the UK. It's from a sample batch that Samsung provided.

I think that I've discovered the problem.... It looks like CrystalDiskMark NVMe v4.1 does not like the 951. If I run the benchmark with v3 then I get the results that I would expect.

Very strange... I wonder what it is about the latest CrystakDiskMark 4 that reacts badly to this SSD.

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