Samsung SM951-NVMe (256GB) PCIe SSD Review
by Kristian Vättö on June 25, 2015 9:40 AM ESTFinal Words
In terms of performance, the NVMe version of the SM951 offers an upgrade over its AHCI sibling. The average data rate (i.e. large IO performance) isn't dramatically better compared to the AHCI version, but when it comes to small IO latency the SM951 and NVMe in general show their might. Typically the NVMe version offers about 10-20% improvement in average latency over the AHCI version, which is a healthy boost in performance given that the two utilize identical hardware.
It's obvious that the SM951-NVMe has been designed for mainstream client workloads. In our Heavy and Light traces it sets new records, but in the most IO intensive The Destroyer trace the SM951-NVMe is outperformed by the SSD 750. While Intel specifically built a client-oriented firmware for the SSD 750, the company made it clear that it focused on sustained random IO performance rather than high peak throughput, and the tradeoff pays off as long as the IO workload is intensive enough (think multiple VMs for instance). Another area where the SSD 750 beats the SM951-NVMe by a substantial margin is steady-state performance, which contributes heavily to The Destroyer benchmark since the trace effectively puts the drive into steady-state.
Speaking of steady-state performance, there are two things I was specifically happy to see in the SM951-NVMe. The first one is the unbelievable IO consistency, which isn't that significant for a client drive but if Samsung can pull off something equivalent (with higher performance, of course) in the enterprise space, then I'll be excited. It never hurts to have that level of consistency in a client drive either, but the it just isn't used to its full potential since client SSDs and workloads are more about peak than sustained performance, which is the opposite of enterprise workloads.
The second part is low queue depth random read performance. This is the area where we haven't seen much improvement in the past few years because ultimately the bottlenecks have been AHCI overhead and NAND latency. Fixing the latter requires a new type of non-volatile memory (e.g. ReRAM, MRAM or NRAM) with significantly lower read latency, but that isn't on the horizon until around 2020. In the mean time, the only way to improve random read latency is to cut the driver stack overhead, which is exactly the purpose of NVMe. The reason why I'm so excited about low queue depth random read performance is the fact that they account for a large of the total IOs in typical client workloads (especially the less intensive ones), so any improvement will translate to better user experience and performance, which is ultimately what a consumer is looking for.
Despite all this, I have to admit that I walk away a little disappointed. A 10-20% performance improvement isn't marginal, but after all the hype about NVMe I was expecting a little more. I have a strong feeling that NVMe is capable of much more, but the technology needs time to mature. From what I have talked to SSD OEMs, the generic NVMe driver that Microsoft includes in Windows 8.1 has some severe shortcomings, which is why nearly everyone has their own custom driver at least for now. I think Samsung and the SM951-NVMe desperately need that to unleash the full potential of the drive and I sure hope that the retail version of the drive will feature one.
All in all, the SSD 750 remains as the best option for very IO intensive workloads, but for a more typical enthusiast the SM951-NVMe provides better performance, although not substantially better than the AHCI version. If you need an SSD today, I wouldn't wait for the NVMe version because the availability is a mystery to all and you may end up waiting possibly months. Nevertheless, if the SM951-NVMe was easily available and reasonably priced, I would give it our "Recommended by AnandTech" award, but for now one can only drool after it.
Facebook
Twitter
RSS
74 Comments
View All Comments
Laststop311 - Friday, June 26, 2015 - link
the pci-e ssd's also improve the 4k qd1/2 as well not by huge amounts but it is faster in that as well.cenpjas - Monday, June 29, 2015 - link
Ignoring OS for the moment, I am not so sure about "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."Currently most people build there own computers are for gaming or specialist use and it is a large market. The advantages of M.2 drives is not just the 4 fold increase in read or 3 fold increase in write speeds over SATA SSD (based on a SM951 VS 850 Evo) but an improved latency over these 'legacy' SSD's. So if your going to throw down £600 for a graphics card would you think twice about a 'mear' £100 more for a 512Gb SM951 VS 500Gb 850 Evo?
For me M.2 is here and now, and SATA SSD's are secondary storage drives. As I build my self very small computers, I like the storage taking up no space in the case. (although I suspect a few small heat sinks in the short term on the drives will need to be the case in a restricted air flow environment). As far as I can tell the SM951-NVMe just makes me more certain that I want it as my primary drive.
As for Win10.0.0 I notice from the Open Beta's that out the box boot support is very good and I can not imagine there being no out the box support for all M.2 type devices, after all, these are OEM for the most part.
epobirs - Thursday, July 2, 2015 - link
You've got to be kidding. An order of magnitude performance increase will become a serious market driver once mainstream availability is there. It's one of those things that has to be experienced to be appreciated. There was a time when SSDs in general seemed like an exotic upgrade for the hot rodders who spent absurd amounts on their systems. Now, I wouldn't consider building a new system without one unless price was the sole priority.There is no reason for the price gap to last beyond this year. Once the chip sets are in production with shippable firmware you're looking at mostly the same same silicon for nearly the entire product. Since prices are very much lower than when SSDs hit the market, PC OEMs aren't faced with the same marketing problems as before. (Though what would remove the final barrier would be for Microsoft to offer functionality comparable to the Apple Fusion Drive in Windows 10.) The cost of having a conventional SATA hard drive for bulk storage alongside a 256-ish GB PCIe SSD for OS and apps is far lower than when the same companies were faced with decisions on how to offer SATA SSDs.
IMHO, the mainstream market will never experience SATA SSD but instead will go direct to PCIe SSDs because that will be the first version the PC OEMs push for mainstream consumers.
dgingeri - Thursday, June 25, 2015 - link
I'd still prefer my 512GB 850 Pro over this.vnangia - Thursday, June 25, 2015 - link
Curious why? Is it just cost-related?I actually recently bought an XP941 to use as a boot drive and have been damn impressed; I needed all the SATA ports for a ZFS array. Even in AHCI mode, it clocked in 850 read/700 write typical, with a peak of 1100/850.
Notmyusualid - Sunday, June 28, 2015 - link
Sounds butt hurt to me...Impulses - Thursday, June 25, 2015 - link
I think I'd like a 256GB SM951 + 1TB 850 EVO setup... Probably going for the latter first tho, my 2x 128GB 830 are definitely getting a little long in the tooth and ditching the games/media drive would be sweet.scan80269 - Thursday, June 25, 2015 - link
Hi Kristian, the Z97 motherboard you used to test SM951 supports only up to PCIe gen2. The SM951 (both AHCI & NVMe versions) support up to PCIe x4 gen3. The sequential read & write figures are lower with the SM951 running at PCIe gen2 compared to gen3. To run SM951 at PCIe gen3 speed you will need an upcoming Intel Skylake platform, with something like Z170 chipset. Even Intel's Broadwell CPUs (like in that NUC) support up to PCIe gen2 only.wyysoft - Thursday, June 25, 2015 - link
Why can’t Z97 support PCIe Gen3? No Z170 chipset is needed to get PCIe Gen3 results.Kristian Vättö - Thursday, June 25, 2015 - link
The SSD is connected directly to the CPU's PCIe lanes and Intel's CPUs have supported PCIe Gen 3 since Ivy Bridge. Skylake and 100-series chipsets will only affect the PCIe lanes coming from the PCH.