Samsung SM951-NVMe (256GB) PCIe SSD Review
by Kristian Vättö on June 25, 2015 9:40 AM ESTRandom Read Performance
For full details of how we conduct our Iometer tests, please refer to this article.
This is the graph I've been dying to see ever since I first heard about NVMe. Random read performance at low queue depths was mostly bottlenecked by AHCI latency because at QD1 the controller can only read from one NAND die (it's asked to read one 4KB chunk of data at a time), meaning that a tremendous share of the latency was caused by the command overhead. As the NVMe command set is much simpler and the whole IO stack is lighter, it opens the doors for improved low queue depth performance, which is exactly what we are seeing with the SM951 NVMe.
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At QD1 the SM951 NVMe offers about 50MB/s, whereas the best AHCI drives I've seen hover around 30-35MB/s, resulting in about 50% gains. Performance at QD2 and QD4 is also better than what other drives offer and in general the SM951 NVMe has excellent random read performance including the high QDs as well.
Random Write Performance
NVMe doesn't present similar gains to random write performance, though. This is an area where Intel clearly has an advantage, but given that the SSD 750 carries an 18-channel controller that is hardly a surprise. Moreover, because the SSD 750 features full power loss protection Intel can cache more user data in the DRAM buffer without the risk of data loss, which can further improve random write performance as IOs can be combined more efficiently. Intel's custom driver may also help with random write performance because the native Microsoft driver has some write performance issues due to Force Unit Access (basically FUA won't consider write to be complete until it has been written to its final medium i.e. NAND, whereas Intel's driver can consider write to be complete when it reaches the DRAM buffer).
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CrazyElf - Thursday, June 25, 2015 - link
@Kristian VättöDoes Windows 10 have better drivers for NVMe SSDs?
It is looking like right now that the SSD 750 might turn out to be the equal of the X-25 SSD in someday popularizing NVMe SSDs.
That being said, for the end consumer I'm not sure it matters as much over a SATA SSD. After all, the typical average user probably values the 4k @QD1/2 above all else, so perhaps these PCI-E SSDs will remain a niche product, unless the price reaches near parity with SATA SSDs, which won't happen for at least a few years.
The big advantage these PCI-E SSDs have is mostly sequential and for write-intensive work.
dgingeri - Thursday, June 25, 2015 - link
Windows 10 is still in development. They're still trying to improve things before the release day. I'm running the 10130 build, and it has many issues. I don't think it would be wise to do any benchmarks under the current Win10 build, and may not be good even under what gets released.hans_ober - Thursday, June 25, 2015 - link
Forget performance/benchmarks, even the UI is unstable. Window manager hangs, quits app. Many issues.Flunk - Thursday, June 25, 2015 - link
Try installing the production gpu drivers. The Beta ones that are automatically installed are quite crashy because they're still working on Direct X 12 support..Gigaplex - Thursday, June 25, 2015 - link
That doesn't apply in my case as I'm using a laptop with Intel graphics that aren't capable of DX12.nathanddrews - Friday, June 26, 2015 - link
Not sure which Intel graphics you have, but I was successful just installing the current 7/8.1 64bit drivers.AlenChakarov - Thursday, June 25, 2015 - link
Huh? Windows 10 has been rock-hard stable for me for quite a while now. Considering it's shipping a month from now, that's how it should be. Is your statement up-to-date?Gigaplex - Thursday, June 25, 2015 - link
I'm running the latest build, and I get a highly visible explorer crash every time I shut down or restart.Notmyusualid - Sunday, June 28, 2015 - link
BS.It is full of holes.
If there is one thing I've learned about software, if Microsoft say Beta, they really do mean it...
kmmatney - Thursday, June 25, 2015 - link
Yeah - I'm running the insider preview, and I'm a bit surprised at how rough things still are. It's stable - it just that a lot of thing don't work smoothly - especially with the App store and Modern Apps. My statement is up to date.