Performance 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 IOPS divided by 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. These results are for all drives 240GB and up.

Steady-State 4KB Random Write Performance

In steady-state 4KB random write performance the EVO is actually slightly faster than the Pro, but given that the EVO employs more over-provisioning (12% vs 7%), it's not out of the ordinary. The 2TB EVO performs slightly lower than the 1TB model, so it seems that despite the upgraded DRAM controller the controller may not be ideal for more than 1TB of NAND (internal SRAM caches and the like are the same as in the MEX controller). Nevertheless, the difference isn't substantial and in any case the Pro and EVO both boast excellent steady-state performance.

Steady-State 4KB Random Write Consistency

Both 2TB drives also have great consistency, although the 2TB Pro can't challenge the 512GB Pro that clearly leads the consistency graph. Given the same amount of raw processing power, managing less NAND is obviously easier because the more NAND there is, the more garbage collection calculations the controller has to process, which results in increased variation in performance.

Samsung 850 Pro 2TB
25% Over-Provisioning

The behavior in steady-state is similar to other 850 Pro and EVO drives, which is hardly surprising given the underlying firmware similarities. One area to note, though, is the increased performance variation with additional over-provisioning (OP), whereas especially the 512GB Pro presents very consistent performance with 25% OP. In any case, performance with additional OP is class-leading in both Pro and EVO.

Samsung 850 Pro 2TB
25% Over-Provisioning
Introduction, The Drives & The Test AnandTech Storage Bench - The Destroyer
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  • SviatA - Friday, August 21, 2015 - link

    As I see it, Samsung is pushing really hard to win over the whole market. The 850 Evo line is a substantial step forward. I really like the way PC starts working with an SSD rather than with HDD.
    I've bought one here
    But you may find even a better offer on eBay, I think. Anyway, even for 85 euro this is a great purchase.
  • htwingnut - Saturday, September 19, 2015 - link

    Can someone please explain the "Performance Consistenty" charts and how to read them? They change every time I switch the default and 25% OP even with the same drives... confusing.
  • - Thursday, October 15, 2015 - link

    I purchased the Samsung SSD 850 Pro to install in my new Windows 10 computer. I can't clone Windows 10 or anything to this drive. I've talked to Samsung for over 7 weeks and keep getting a new date for the release of their cloning software. I've tried 2 different cloning software and they don't work with this drive. Until Samsung updates the software for Windows 10 DON'T BUY.
  • Miller1331 - Tuesday, December 1, 2015 - link

    Using 2 of these in a music production rig and they are monsters
  • Meteor2 - Wednesday, November 23, 2016 - link

    I don't think this reviews specifies what interface the 850 Pro uses anywhere.
  • Meteor2 - Wednesday, November 23, 2016 - link

    ...until the last page. Would've thought it page 1 material, myself.

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