Performance Consistency

Our performance consistency test explores the extent to which a drive can reliably sustain performance during a long-duration random write test. Specifications for consumer drives typically list peak performance numbers only attainable in ideal conditions. The performance in a worst-case scenario can be drastically different as over the course of a long test drives can run out of spare area, have to start performing garbage collection, and sometimes even reach power or thermal limits.

In addition to an overall decline in performance, a long test can show patterns in how performance varies on shorter timescales. Some drives will exhibit very little variance in performance from second to second, while others will show massive drops in performance during each garbage collection cycle but otherwise maintain good performance, and others show constantly wide variance. If a drive periodically slows to hard drive levels of performance, it may feel slow to use even if its overall average performance is very high.

To maximally stress the drive's controller and force it to perform garbage collection and wear leveling, this test conducts 4kB random writes with a queue depth of 32. The drive is filled before the start of the test, and the test duration is one hour. Any spare area will be exhausted early in the test and by the end of the hour even the largest drives with the most overprovisioning will have reached a steady state. We use the last 400 seconds of the test to score the drive both on steady-state average writes per second and on its performance divided by the standard deviation.

Steady-State 4KB Random Write Performance

The RD400 sustains good random write performance, but the controllers and firmware in the OCZ Vector 180 and Intel 750 were designed with this kind of test in mind, and it shows. PCIe and NVMe don't help appreciably when the performance bottleneck is all the bookkeeping inside the controller, but NVMe controllers tend to have at least adequate processing power.

Steady-State 4KB Random Write Consistency

Most Samsung and Intel drives are much more consistent than the RD400, but the latter's score is fine for a client drive.

IOPS over time
25% Over-Provisioning

The 512GB RD400 shows oddly different behavior from the other two capacities when tested with overprovisioning, but the RD400 results are all good looking with no extremely low performance outliers.

Steady-State IOPS over time
25% Over-Provisioning

The minimum random write performance of the RD400 is as good as the average performance of most SATA drives. There is some periodic variation apparent for the 512GB and 1TB models in the form of steep drops that last only a few seconds.

Introduction AnandTech Storage Bench - The Destroyer


View All Comments

  • AnnonymousCoward - Wednesday, May 25, 2016 - link

    What about boot time. Is it slow like the Intel card? Reply
  • mervincm - Wednesday, May 25, 2016 - link

    Intel 750 SSD isn't slow at boot anymore. Later SSD firmware and NVME drivers have really helped my boot performance. Reply
  • Yregister - Thursday, November 3, 2016 - link

    But that's on Windows, correct? I read that the 750 doesn't work on a Mac, not bootable... Reply
  • moheban79 - Saturday, November 12, 2016 - link

    Thats not true. I got my Intel 750 booting up my hackintosh. Should be doable. Reply
  • adamto - Wednesday, May 25, 2016 - link

    Why there is no 2T or even 4T M.2 SSD? Reply
  • Silma - Wednesday, May 25, 2016 - link

    Because there isn't enough place on the stick. One would need to develop much denser NAND. Reply
  • Billy Tallis - Wednesday, May 25, 2016 - link

    A double-sided M.2 2280 can usually fit four packages of flash, each containing a stack of up to 16 dies that are typically 128Gb (16GB). That multiplies out to a practical limit of 1024GB for now. Newer 3D NAND such as Micron's will be available in 256Gb MLC dies, enabling 2TB M.2 2280 drives (or 3TB with TLC). Reply
  • Dr.Neale - Wednesday, May 25, 2016 - link

    Don't you mean 4 TB with TLC? Reply
  • Billy Tallis - Wednesday, May 25, 2016 - link

    We're not quite there yet. Micron's 3D TLC is 384Gb and everybody else seems to be going for a 256Gb TLC that will be a smaller die than their 256Gb MLC. A 4TB M.2 would require either a 512Gb die or denser packaging. Reply
  • Chaser - Wednesday, May 25, 2016 - link

    "Upgrading from a mechanical hard drive to a SSD alleviates a major performance bottleneck but the experience of moving from SATA SSDs to PCIe SSDs is not as revolutionary. I suspect most consumers would be better served with a larger SSD of moderate performance than a cramped but blazing fast PCIe drive," Thank you! Reply

Log in

Don't have an account? Sign up now