Samsung SM951 PCIe M.2 512GB SSD Review

A Closer Look at the SM951

Our Samsung SM951 512GB drive arrived in a Lenovo X1 Carbon Gen 3, so we don't have a retail package to show you.

The notch cut into the lower end of the connector shown above is called a M key. A notch cut out of the top is called a B key. Some products have both M and B keys, but the SM951 only supports PCIe, so it has the M key. Your motherboard or PCIe-to-M.2 adapter will have one or the other as well. It's important to choose the right SSD for your platform, or at least the correct adapter.

With its label removed, we can see the component layout of the SM951 512GB. The drive uses a new controller paired with 16nm MLC flash, both manufactured and designed by Samsung. The company also uses a DRAM package to buffer page table data.

There are four NAND packages on the 512GB version, two on each side. Samsung doesn't put any flash directly opposite the controller. It's particularly sensitive to heat, and writes to flash running outside of a specified temperature range cuts into cell endurance.

The XP941's controller reached as high as 100 °C during long synthetic random write tests. Fortunately, the new UBX controller tames those high temperatures. Samsung does not disclose what lithography node its controllers are manufactured on, but we suspect the UBX employs smaller transistors than the XP941's UAX controller.

Without NVMe, the UBX controller is a generational update of the product it replaces. Both the XP941 and SM951 use the AHCI command set to communicate with the host. The edge connector is also the same, even though the newer model takes advantage of PCIe 3.0. Samsung did initially announce its SM951 as NVMe-capable, but that was later revised down to AHCI for January's release.

This is our first look at Samsung's 2D planar NAND on 16nm lithography. We suspect OEMs didn't want to pay extra for the company's 3D V-NAND technology. The smaller process means that Samsung can produce more die per wafer, a quick and easy way to reduce costs. 

This is the inside of the Lenovo X1 Carbon Gen 3. There are three slots for add-in cards. Two are populated, but only one accepts a double-sided storage card. We're testing both SATA- and PCIe-based M.2 cards in the system (the XP941 works in Lenovo's X1 Carbon Gen 3 as well).

This thread is closed for comments
51 comments
    Your comment
  • 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???
  • JOSHSKORN
    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.

    Ian.
  • 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 newegg.com in the Enterprise SSD section. I want one!
  • generalsheep
    Is this little bastard bootable,so i can use it as my maindrive?
  • CyranD
    I have my eye on purchasing a Sager NP8652 in the near future. Currently they list Samsung XP941 as a option. I am hoping before am ready to buy they add the Samsung SM951 as a option.

    Quote:
    Is this little bastard bootable,so i can use it as my maindrive?


    Sager let you set the Samsung XP941 as the boot drive so I assume the SM951 can be used as a boot drive.
  • Blueberries
    I would have liked to see the 850 Pro included in this as well
  • CRamseyer
    I didn't need an adapter to test this product. The ASRock Z97 Extreme6 has a M.2 x4 slot that connects directly to the CPU.

    Yes, this product is bootable. The only modern PCIe SSD that is not bootable is from Fusion-IO.
  • wolfy747400
    Any ideas why this SSD performed a little faster on some tests on a Intel Z68 Express-based motherboard than the Z97?
  • kyuuketsuki
    While the drive's performance is certainly impressive, the serving time graph shows what you really need to know: the performance will make practically no difference in the vast majority of consumer workloads. The only people who should be spending the premium for this drive are professionals who will regularly be transferring large files around. Anyone else is just wasting money, as any modern SSD will perform largely the same in practice, even if their benchmark numbers aren't as impressive.
  • damric
    I am interested in M2 since my motherboard has a slot for one. Do they work as boot drives yet? I haven't been following closely but last time I checked they did not.
  • RamCity
    Quote:
    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?


    Sadly neither the SM951 or XP941 are compatible upgrades in the MacBook Air or the current cylindrical Mac Pro as the standard M.2 interface connector is different from the one that Apple use. Older Mac Pro towers are fine with the use of a standard PCIe to M.2 adapter card.
  • RamCity
    Quote:
    I am interested in M2 since my motherboard has a slot for one. Do they work as boot drives yet? I haven't been following closely but last time I checked they did not.


    Most 'modern' motherboards with Z97/H97 or X99 chipsets can boot the XP941 and likely the SM951 as well, so long as your bios is up to date. Also, like Chris mentioned in the article, you'll also typically need to install windows from a USB drive.
  • CRamseyer
    Yes, they work as a boot drive.
  • damric
    1901805 said:
    Quote:
    I am interested in M2 since my motherboard has a slot for one. Do they work as boot drives yet? I haven't been following closely but last time I checked they did not.
    Most 'modern' motherboards with Z97/H97 or X99 chipsets can boot the XP941 and likely the SM951 as well, so long as your bios is up to date. Also, like Chris mentioned in the article, you'll also typically need to install windows from a USB drive.


    1888934 said:
    Yes, they work as a boot drive.


    Thanks. I might pick one up for my ASUS Z97I-PLUS.
  • bit_user
    *yawn* I just clicked for some tasty NVMe benchmarks. Should have mentioned it's AHCI-only, sooner.
  • hst101rox
    4K random reads/writes aren't any better than SATA 3 SSDs so as an OS drive I don't see an advantage. For mass storage/large files, sure.
  • CRamseyer
    This drive has the highest 4K QD1 random read from a consumer SSD available today, over 12K IOPS. It has the highest QD2 and QD4 as well. Most of us will never get beyond QD8 under normal use. The 4K random writes are really good too.

    A better metric to look at is on page 4, the mixed workload tests. You will never just read or just write data with an OS drive.
  • Markor
    I don't want to use google.com and gooleapis Javascripts, just to be able to turn article pages , read articles without obstructions and privately use the site!
    Remove need to use googleapis and google.com Javascripst from your site(s) for basic functions, if you want me to read your articles and coem again!