The Samsung SSD 850 EVO mSATA/M.2 Review
by Kristian Vättö on March 31, 2015 10:00 AM ESTPerformance Consistency
We've been looking at performance consistency since the Intel SSD DC S3700 review in late 2012 and it has become one of the cornerstones of our SSD reviews. Back in the days many SSD vendors were only focusing on high peak performance, which unfortunately came at the cost of sustained performance. In other words, the drives would push high IOPS in certain synthetic scenarios to provide nice marketing numbers, but as soon as you pushed the drive for more than a few minutes you could easily run into hiccups caused by poor performance consistency.
Once we started exploring IO consistency, nearly all SSD manufacturers made a move to improve consistency and for the 2015 suite, I haven't made any significant changes to the methodology we use to test IO consistency. The biggest change is the move from VDBench to Iometer 1.1.0 as the benchmarking software and I've also extended the test from 2000 seconds to a full hour to ensure that all drives hit steady-state during the test.
For better readability, I now provide bar graphs with the first one being an average IOPS of the last 400 seconds and the second graph displaying the standard deviation during the same period. Average IOPS provides a quick look into overall performance, but it can easily hide bad consistency, so looking at standard deviation is necessary for a complete look into consistency.
I'm still providing the same scatter graphs too, of course. However, I decided to dump the logarithmic graphs and go linear-only since logarithmic graphs aren't as accurate and can be hard to interpret for those who aren't familiar with them. I provide two graphs: one that includes the whole duration of the test and another that focuses on the last 400 seconds of the test to get a better scope into steady-state performance.
For a mainstream drive, the 850 EVO mSATA/M.2 does relatively well in IO consistency except for the highest capacity 1TB model. Strangely enough the 2.5" 1TB 850 EVO does just fine, so this issue seems to be limited to the mSATA version.
Looking at the standard deviation reveals why: the IO consistency of the 850 EVO mSATA 1TB, even with overprovisioning, is horrible compared to the rest of the 850 EVO lineup.
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The issue with the 1TB mSATA is actually worse than I expected because it's literally stopping for seconds in a frequent manner. The pauses can even be over 50 seconds, so this isn't just some normal garbage collection that's happening in the background. I find this to be very alarming because it may have dramatic impact to user experience and it's simply something that no modern SSD should do anymore. I did let Samsung know about my findings before publishing this review, but I wasn't really able to get any comment from them regarding this issue and whether Samsung has noticed something similar in its internal tests. Adding over-provisioning seems to help as the pauses become much more infrequent, but for now I would still advise against buying the 1TB mSATA version until there's a fix for the IO consistency.
As for the other capacities, the 850 EVO has excellent consistency and steady-state performance for a mainstream drive. The capacity has some effect on performance, but even the 250GB model has roughly twice the performance of 240GB Ultra II thanks to faster V-NAND.
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Laststop311 - Wednesday, April 1, 2015 - link
Was really disappointed with the 1TB results. Also disappointed no ultra m2 interface. I wont be upgrading until I can get a pci-e 3.0 x4 interface on the drive. The samsung sm951 is where its at.Laststop311 - Wednesday, April 1, 2015 - link
Really annoying that I dont see this drive for sale anywhere and it's been talked about for a loooong timeKristian Vättö - Wednesday, April 1, 2015 - link
RamCity just got its first SM951 batch, so it's now available for purchase.https://www.ramcity.com.au/upgrade/data-storage/in...
bricko - Thursday, April 2, 2015 - link
Is the 951 NVMe - How to they compare to the new Intel 750 series which are PCIe gen 3 and NVMeseen here
http://linustechtips.com/main/topic/340041-intel-l...
http://forums.overclockers.co.uk/showthread.php?p=...
Intel are launching the new 750 Series range of SSD's these are PCI-E 3.0 versions with 4 lanes and are NVMe based SSD's
goodyes - Wednesday, April 1, 2015 - link
Ya, but results that I have a 1TB 840 msata and write sequential at more than 500MBps around 520max MBps, and now I see than new 850 msata tops at ?? 480MBps ?? cannot be possible what my eyes look, AND WHY THE HELL NO ONE REVIEWER COMPARE With olders 840 msata, so I must think that all of you guys are a paid reviewers and you get money from samsung, if not, YOU MUST compare to older modelKenPC - Wednesday, April 1, 2015 - link
I am seriously concerned that the 840 evo, and TLC in general may indeed have an uncurable problem with slowdown after a period of time. This same problem has also been reported in multiple instances for Samsung OEM drives based on the 840 evo TLC technology.GIven that the 850 evo msata line was delayed by Samsung by about a month, it might be possible that the Anandtech review units were actually tested in late Feb and the go-ahead to publish the results only recently provided.
I did also notice that the estimated 'March" timeframe for a new 840 evo firmware has come and passed, as well as no drive magician support for the 850 evo m2/msata drives yet.
Anandtech results for the 1TB 850 evo unit are also quite concerning.
So, I also join the crowd asking for a look at the 850 evo 2.5 and msata drives after some time has passed to see if they suffer from the slowdown problem too.
And a rhetorical, but serious question - does anybody actually have a Samsung TLC drive that has NOT suffered from the slowdown as measured by the proper tools a few months after the drive was formatted/set up?
And kudos to Anandtech - for an SSD review that really tests the drives, not just a run of ATTO or such.
Per Hansson - Wednesday, April 1, 2015 - link
"anything that taxes the drive a bit more may run into the issue, which is basically that the drive stops for up to dozens of seconds (i.e. your system freezes). Until Samsung fixes that, I would advise against buying the 1TB version unless you have a very light workload (web browsing, email, etc.). I suspect it's fixable through a firmware update, but I'll have to wait for Samsung's reply to be sure of that."A wise man once said: if you wait for a firmware fix for your Samsung SSD's you will wait a long time.
He died of old age.
RIP Samsung 840 TLC drives.
Dzungpv - Friday, April 3, 2015 - link
Missing Temperature when idle, full load or stretch, i want this information before buy them .szhosain - Sunday, April 5, 2015 - link
As far as I can tell, you only tested the M.2 version of the Samsung 850 EVO in a 500GB size.Can we assume that the MSATA version of that drive and size will perform essentially identically?
voicequal - Monday, April 13, 2015 - link
Good catch on the poor mSATA 1TB performance during the performance consistency test. It harkens back to the early Jmicron stuttering days. I was similarly affected by the SanDisk U100 a few years ago. The system freezes, particularly when swap file is active, and disk throughput drops to low single digit MB/s. Hard to believe the most modern SSDs can still get into this state. Vanilla benchmarks don't show the problem.