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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Notmyusualid - Sunday, June 28, 2015 - link
I'm SO with you on that statement. My 840 Evos have been awful. TLC is not for me, and I don't care what benchies you throw at me, I won't buy TLC nand now from anybody.Notmyusualid - Sunday, June 28, 2015 - link
Sorry, just noticed this is MLC and not TLC. Well, still going to be buyer-beware due to my last experience of slow down, firmware revisions etc with Samsung...Impulses - Tuesday, July 21, 2015 - link
There's not one SSD OEM that hasn't suffered some sorta critical firmware bug, and many have suffered thru more of it than Samsung and/or hardware defects...Crucial had some bricked drives, as did Intel using their own controller, never mind their Sandforce drive which had broken encryption, I'm more concerned about how they react and respond.
Samsung wasn't brilliant at it from what I've seen, but they did keep re issuing updates so at least they stuck with it. The fact that they ignored the non EVO (which few seem to bring up) seems the most egregious error to me.
The newest iteration of 3D TLC is quite a different animal anyway... I've had two Intel drives, two 128GB 830s, bought a 500GB 840 EVO as a gift, just bought a 1TB 850 EVO, and I'll probably get a 256GB SM951. /shrug
Romney4President - Friday, June 26, 2015 - link
What the heck...? No Encryption... :/ Can anyone shed some light on this? If I remember right other manufactures coming out with NVMe will be supporting hardware based encryption. This is a deal breaker to me. Also do you think later this year we'll see a Samsung version with encryption?Perk5 - Monday, June 29, 2015 - link
Can this SM951nvme be used at full speed with asrockextreme6 z97 mobo, which has ultra m.2 slot. also the ahci model of sm951 has been sucessfully used as boot drive at full speed by many users having this mobo. And are there any drawbacks of the asrock mobo ?boe - Tuesday, June 30, 2015 - link
Just bring on those 10TB and 32TB SSD drives. I need them like yesterday.JKJK - Sunday, July 12, 2015 - link
It seems that there is a firmware update that makes the drive handle fua more effectively:http://www.legitreviews.com/samsung-sm951-nvme-m-2...
Impulses - Tuesday, July 21, 2015 - link
They got a second drive with updated firmware, no word about an actual update, being mostly OEM drives they might've not even built in a way to update the firmware...JoKO4184 - Monday, July 20, 2015 - link
So, if both the AHCI and NVMe have the same hardware, do you guys reckon we'd be able to flash the NVMe firmware onto the AHCI? Or at least if Samsung feels generous enough to provide the upgrade for all AHCI owners?caelumtech - Thursday, August 27, 2015 - link
If the two variants are so similar, what prevents them from being "flash" compatible? Could an intrepid hacker Download the firmware from the NVME device and overwrite the flash of the AHCI version?