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 4TB 850 EVO restores a little bit of the performance that the 2TB lost relative to the 1TB, but Samsung's controller architecture is still clearly most comfortable at 1TB.

Steady-State 4KB Random Write Consistency

The consistency of the 2TB 850 EVO was only slightly better than the 1TB EVO, so it's surprising to see the 4TB model make such a large jump and come so close to the 1TB 850 Pro.

IOPS over time
25% Over-Provisioning

It is no surprise that a 4TB drive lasts so long before dropping out of peak performance: it has far more spare area to burn through than any ordinary consumer SATA SSD. The transition to steady state is uncharacteristically long and messy for a Samsung drive, and the performance lows during this period are disappointing. Once the drive has reached steady state, there's nothing to complain about.

Steady-State IOPS over time
25% Over-Provisioning

There are no wild outliers from the 4TB 850 EVO's steady-state, and none of the longer-term drift in performance shown by the 1TB and 2TB 850 EVO and Pro models. With extra overprovisioning, the 4TB EVO carries on indefinitely with high and extremely steady performance.

Introduction AnandTech Storage Bench - The Destroyer


View All Comments

  • no_nonsense4857 - Wednesday, July 13, 2016 - link

    Was always interested in a higher capacity M.2 drive for my XPS13. 850 Evo maxed out at 512GB where as the Sandisk X400 was the only reliable one at 1TB.

    Amazon has just listed a 850 Evo 1TB M.2 @ 350 USD - So eagerly waiting for an update from Anand in this regards :)
  • zodiacfml - Thursday, July 14, 2016 - link

    Though SATA interface is limiting the performance of such drives, isnt Random performance has more room to grow? Reply
  • hMunster - Saturday, July 16, 2016 - link

    The write endurance is really shit at only 75 writes. How large are the pages, and how much is typical write amplification, or is that already factored in? Reply
  • NomadXL - Wednesday, July 27, 2016 - link

    So this new 850 EVO 4TB has a 300 Endurance.. and the previous one of 2TB aswell?

    I thought the 2TB model had only a 150TB endurance rating..

    Please can somebody confirm this?
  • centaur1 - Thursday, July 28, 2016 - link

    Any idea of external cases that this will work with? Thunderbolt? Reply

Log in

Don't have an account? Sign up now