The Toshiba OCZ VX500 (256GB, 512GB, 1024GB) SSD Reviewby Billy Tallis on September 13, 2016 9:00 AM EST
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.
No consumer SATA drive sustains better random write IOPS than the Vector 180, while the VX500 is slower than most MLC drives.
The Barefoot 3 controller wasn't great for consistency in spite of its high overall performance, so the Vector 180 and VX500 end up with relatively similar scores, and both have lots of room for improvement.
The VX500 goes through two distinct performance phases before reaching steady-state. During those early phases it maintains relatively good minimum performance, in stark contrast to the severe stuttering the Vector 180 showed throughout this test, especially for the larger capacities.
With extra manual overprovisioning, the VX500 goes through several more phase transitions but always maintains decent performance.
The steady state write performance of the VX500 is confined mostly to a band around 3k-5k IOPS with frequent outliers up to about twice that speed. With extra overprovisioning, the steady state is clearly better than that of the Phison-based PNY CS2211 but not as fast or consistent as the flagship MLC drives from Samsung and SanDisk.