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 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.

Steady-State 4KB Random Write Performance

Barefoot 3 has always done well in steady-state performance and the Vector 180 is no exception. It provides the highest average IOPS by far and the advantage is rather significant at ~2x compared to other drives.

Steady-State 4KB Random Write Consistency

But on the down side, the Vector 180 also has the highest variation in performance. While the 850 Pro, MX100 and Extreme Pro are all slower in terms of average IOPS, they are a lot more consistent and what's notable about the Vector 180 is how the consistency decreases as the capacity goes up. 

OCZ Vector 180 240GB
Default
25% Over-Provisioning

Looking at the scatter graph reveals the source of poor consistency: the IOPS reduce to zero or near zero even before we hit any type of steady state. This is known behavior of the Barefoot 3 platform, but what's alarming is how the 480GB and 960GB drives frequently drop to zero IOPS. I don't find that acceptable for a modern high-end SSD, no matter how good the average IOPS is. Increasing the over-provisioning helps a bit by shifting the dots up, but it's still clear that 240GB is the optimal capacity for Barefoot 3 because after that the platform starts to run into issues with consistency due to metadata handling.

OCZ Vector 180 240GB
Default
25% Over-Provisioning
SSD Guru: The New OCZ Toolbox AnandTech Storage Bench - The Destroyer
POST A COMMENT

89 Comments

View All Comments

  • Guspaz - Tuesday, March 24, 2015 - link

    Well, one person in particular had difficulty remembering the proper saying while in Tennessee... Reply
  • Minion4Hire - Tuesday, March 24, 2015 - link

    He's quoting George Bush. Reply
  • mapesdhs - Wednesday, March 25, 2015 - link

    And hence not exactly a viable rationale for concluding anything about anything.

    Ian.
    Reply
  • CaedenV - Tuesday, March 24, 2015 - link

    Cant beat the Evo on price, performance, or support... so then what is the point? Reply
  • kmmatney - Tuesday, March 24, 2015 - link

    None of the benchmarks include the EVO, so it's hard to tell if it beats it or not. It is probably faster, but the MSRP is the same as the 850 Pro, which definitely beats it in most tests. Reply
  • ocztosh - Tuesday, March 24, 2015 - link

    Hi CaedenV, thank you for your feedback. The Vector 180 is designed for the high performance/workstation market and is not positioned versus the TLC based EVO. When it comes to best balance of performance/value our ARC series (based on MLC). We will be coming out with future products that push the value envelope that leverage Toshiba TLC. Reply
  • mapesdhs - Wednesday, March 25, 2015 - link

    I was impressed with the Arc 100, it was quicker than I expected. Any data yet on return
    rates? It would be interesting to know if it's been competitive with the 850 EVO in that regard.
    Samsung has a strong reputation here. My main concern with the Vector 180 though is it will
    appear too expensive compared to the 850 Pro and SanDisk Extreme Pro.

    Ian.
    Reply
  • chrnochime - Tuesday, March 24, 2015 - link

    The point is some ppl don't actually want to use TLC. Reply
  • ocztosh - Wednesday, March 25, 2015 - link

    Hi chrnochime, thank you for your comments. We so agree there are still a lot of customers that would still prefer MLC. Our current value drive series is MLC based and even after we introduce a TLC based Series we will continue to deliver MLC drives for those customers that are looking for drives higher up the performance spectrum. Reply
  • chrnochime - Tuesday, March 24, 2015 - link

    Support? So how long did that TLC fix take to be available again? Reply

Log in

Don't have an account? Sign up now