Performance Consistency

In our Intel SSD DC S3700 review Anand introduced a new method of characterizing performance: looking at the latency of individual operations over time. The S3700 promised a level of performance consistency that was unmatched in the industry, and as a result needed some additional testing to show that. The reason we don't have consistent IO latency with SSDs is because inevitably all controllers have to do some amount of defragmentation or garbage collection in order to continue operating at high speeds. When and how an SSD decides to run its defrag and cleanup routines directly impacts the user experience. Frequent (borderline aggressive) cleanup generally results in more stable performance, while delaying that can result in higher peak performance at the expense of much lower worst-case performance. The graphs below tell us a lot about the architecture of these SSDs and how they handle internal defragmentation.

To generate the data below we take a freshly secure erased SSD and fill it with sequential data. This ensures that all user accessible LBAs have data associated with them. Next we kick off a 4KB random write workload across all LBAs at a queue depth of 32 using incompressible data. We run the test for just over half an hour, nowhere near what we run our steady state tests for but enough to give a good look at drive behavior once all spare area fills up.

We record instantaneous IOPS every second for the duration of the test and then plot IOPS vs. time and generate the scatter plots below. Each set of graphs features the same scale. The first two sets use a log scale for easy comparison, while the last set of graphs uses a linear scale that tops out at 40K IOPS for better visualization of differences between drives.

The high level testing methodology remains unchanged from our S3700 review. Unlike in previous reviews however, we vary the percentage of the drive that gets filled/tested depending on the amount of spare area we're trying to simulate. The buttons are labeled with the advertised user capacity had the SSD vendor decided to use that specific amount of spare area. If you want to replicate this on your own all you need to do is create a partition smaller than the total capacity of the drive and leave the remaining space unused to simulate a larger amount of spare area. The partitioning step isn't absolutely necessary in every case but it's an easy way to make sure you never exceed your allocated spare area. It's a good idea to do this from the start (e.g. secure erase, partition, then install Windows), but if you are working backwards you can always create the spare area partition, format it to TRIM it, then delete the partition. Finally, this method of creating spare area works on the drives we've tested here but not all controllers are guaranteed to behave the same way.

The first set of graphs shows the performance data over the entire 2000 second test period. In these charts you'll notice an early period of very high performance followed by a sharp dropoff. What you're seeing in that case is the drive allocating new blocks from its spare area, then eventually using up all free blocks and having to perform a read-modify-write for all subsequent writes (write amplification goes up, performance goes down).

The second set of graphs zooms in to the beginning of steady state operation for the drive (t=1400s). The third set also looks at the beginning of steady state operation but on a linear performance scale. Click the buttons below each graph to switch source data.

  OCZ Vertex 460 240GB OCZ Vector 150 240GB Corsair Neutron 240GB Sandisk Extreme II 480GB Samsung SSD 840 Pro 256GB
Default
25% OP

Performance consistency is more or less a match with the Vector 150. There is essentially no difference, only some slight variation which may as well be caused by the nature of how garbage collection algorithms work (i.e. the result is never exactly the same). 

  OCZ Vertex 460 240GB OCZ Vector 150 240GB Corsair Neutron 240GB SanDisk Extreme II 480GB Samsung SSD 840 Pro 256GB
Default
25% OP

 

  OCZ Vertex 460 240GB OCZ Vector 150 240GB Corsair Neutron 240GB SanDisk Extreme II 480GB Samsung SSD 840 Pro 256GB
Default
25% OP

TRIM Validation

To test TRIM, I first filled all user-accessible LBAs with sequential data and continued with torturing the drive with 4KB random writes (100% LBA, QD=32) for 60 minutes. After the torture I TRIM'ed the drive (quick format in Windows 7/8) and ran HD Tach to make sure TRIM is functional.

And TRIM works. The HD Tach graph also shows the impact of OCZ's performance mode, although in a negative light. Once half of the LBAs have been filled, all data has to be reorganized. The result is a decrease in write performance as the drive is reorganizing the existing data at the same time as HD Tach is writing to it. Once the reorganization process is over, the performance will recover close to the original performance.

Introduction, The Drive & The Test AnandTech Storage Bench 2013
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  • dgingeri - Wednesday, January 22, 2014 - link

    This thing has the same problem as my Vertex 4 drives. I'm not impressed. It essentially means that half the capacity is unusable due to the way the controller works. Reply
  • Guspaz - Wednesday, January 22, 2014 - link

    Hrrm. Getting merged into Toshiba's SSD group is about the only thing that might have tempered my "never again" position on OCZ. By keeping them independent, they're doing nothing to convince me that they're going to change their ways. It's their own questionable decisions that got them into this mess (their reputation for poor reliability), sacrificing reliability at the alter of performance and shipping first. Reply
  • dgingeri - Wednesday, January 22, 2014 - link

    You think the Toshiba name is good reliability? I have 224 enterprise hard drives that would say differently. Four years ago, I got 204 Fujitsu/Toshiba (just after Toshiba took over) 146GB 15k SAS drives. Over the course of the first three years, I replaced 165 of them, plus 19 of the replacements that came in as Toshiba branded drives with the same model number. After the warranty ended, I have had to replace the remaining ones by purchasing new ones. None of them are left now. All have been replaced with Seagate Saavios of the same size. They are worse than any desktop level hard drives I have dealt with in my career. I've only had one incident like it, and that was replacing Dell Optiplex motherboards with embedded TNT2-m64 chips back in 2000. Reply
  • Guspaz - Wednesday, January 22, 2014 - link

    Seagate has rather questionable reliability themselves (see BackBlaze's recent study on this), but Toshiba's hard disk division is unrelated to their SSD division, so the reliability of one doesn't necessarily give any indication about the reliability of the other. Reply
  • dgingeri - Wednesday, January 22, 2014 - link

    In the 2.5" enterprise hard drive market, Seagate has been top of the heap for a long time. They really do well in that arena. There aren't a whole lot of players in that arena, though. Only Seagate, Toshiba (formerly Fujitsu,) and Hitachi. Seagate's Saavio line happens to be the first line ever in 2.5" 10k or 15k drives.

    As far as desktop drives go, Seagate's desktop drives have had reliability problems for years, sure, but they aren't near as bad as Toshiba's desktop drives.
    Reply
  • Dahak - Wednesday, January 22, 2014 - link

    Wonder if ocz will use/can use toshiba's ssd team for addition support(firmware/validation)even though they are separate entities

    Also found it funny that while reading this review I had ads for Crucial's SSD :)
    Reply
  • MrSpadge - Wednesday, January 22, 2014 - link

    Otherwise the aquisition wouldn't make much sense, would it? Keep them somewhat separate but use any synergetic benefits. Reply
  • Dahak - Wednesday, January 22, 2014 - link

    I would think so too but the way it is worded in the article seems like they wont Reply
  • piroroadkill - Wednesday, January 22, 2014 - link

    Why don't you just review a rock or a potato? Because I doubt many people want to purchase OCZ products. Reply
  • toyotabedzrock - Wednesday, January 22, 2014 - link

    It might be a good idea to not copy and paste the same explanation of the tests in every article.

    Just link to the information. It is just headache inducing that I have hunt for relevant information interleaved with the copy and pasted parts.
    Reply

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