Samsung SM951 (512GB) PCIe SSD Review
by Kristian Vättö on February 24, 2015 8:00 AM ESTMixed Random Read/Write Performance
Mixed read/write tests are also a new addition to our test suite. In real world applications a significant portion of workloads are mixed, meaning that there are both read and write IOs. Our Storage Bench benchmarks already illustrate mixed workloads by being based on actual real world IO traces, but until now we haven't had a proper synthetic way to measure mixed performance.
The benchmark is divided into two tests. The first one tests mixed performance with 4KB random IOs at six different read/write distributions starting at 100% reads and adding 20% of writes in each phase. Because we are dealing with a mixed workload that contains reads, the drive is first filled with 128KB sequential data to ensure valid results. Similarly, because the IO pattern is random, I've limited the LBA span to 16GB to ensure that the results aren't affected by IO consistency. The queue depth of the 4KB random test is three.
Again, for the sake of readability, I provide both an average based bar graph as well as a line graph with the full data on it. The bar graph represents an average of all six read/write distribution data rates for quick comparison, whereas the line graph includes a separate data point for each tested distribution.
Quite surprisingly the SM951 and Samsung drives in general don't do very well with mixed data.
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The reason lies in the fact that the performance of Samsung drives plummets when the share of writes is increased. At 80/20 read/write, the Samsung drives manage to do pretty well, but after that the performance declines to about 40MB/s. What's odd is that the performance is also bad with 100% writes, whereas with other drives we usually see a spike here. I'm guessing there's some garbage collection going on here that causes the performance degradation.
Mixed Sequential Read/Write Performance
The sequential mixed workload tests are also tested with a full drive, but I've not limited the LBA range as that's not needed with sequential data patterns. The queue depth for the tests is one.
With 128KB sequential data, however, the SM951 is the king of the hill. There's a clear difference between PCIe and SATA based drives, although it's worthy to note that the difference is mostly due to PCIe drives having much higher throughput at 100% reads and writes (i.e. the infamous bathtub curve).
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Kristian Vättö - Tuesday, February 24, 2015 - link
PCIe adapters are fine for review purposes and are in fact more easily serviceable than M.2 slots tend to be.Samus - Tuesday, February 24, 2015 - link
Thank you for pointing out all capacities are M2 2280 DOUBLE SIDED. That is missing from virtually all reviews, sales material and eCommerce sites for M2 drives. Newegg has been pretty good about taking pictures of both sides of many drives, though.This is important to me because I work with HP Elitebook's and the newest generation of the Elitebook 810 (G2) and 820\1040 all require single-sided. The 840 has room for M2 DS modules, though.
Flash13 - Tuesday, February 24, 2015 - link
The company is not trustworthy! Buy at your own risk. Good Luck.youtard - Tuesday, February 24, 2015 - link
hurr!Wardrop - Tuesday, February 24, 2015 - link
Does this form factor work in standard desktop PCI-e 4x slots?DanNeely - Tuesday, February 24, 2015 - link
It's an m-2 plug, you need an adapter to fit it in a standard pcie slot.wtallis - Wednesday, February 25, 2015 - link
When discussing NVMe, please make it clear that the chipset and motherboard firmware only matter for booting off the drive; they don't need any updates to allow a compatible operating system to access the drive as something other than the boot volume.(As for what the motherboard firmware needs to gain in order to allow booting from NVMe devices, it's just a loadable UEFI device driver. Even if your motherboard doesn't have such a driver built-in, you could load it from some other storage device and then boot off the NVMe drive.)
ericgl21 - Wednesday, February 25, 2015 - link
I wonder if Samsung (or any other OEM) would be willing to sell a 1TB m.2 NVMe PCIe3.0 x4 SSD with SLC NAND with a 2280 form factor?Many professionals would appreciate the speed and reliability that SLC NAND provides.
Sure, it would cost a lot, but so do the Samsung SM951 and Intel P3700.
If that's not possible with current 16nm manufacturing, then a 512GB would also be nice. :-)
Just my 2 cents.
baii9 - Wednesday, February 25, 2015 - link
reliable on nand? Reliable controller matters, high endurance nand matters, I think nand are "reliable' enough already(compare to that lovely controller).IlikeSSD - Wednesday, February 25, 2015 - link
looks like Samsung paid for not showing OCZ in consistency and mixed workload tests )))))