Four-Corner Testing
The basic four corners of storage testing include sequential reads, sequential writes, random reads and random writes. Not every reviewer or company tackles these the same way.
Sequential data is usually measured with 128KB blocks, though some editors like to use 64KB and others go as high as 8MB blocks. For the most part, we use 128KB, but also publish a single-drive chart that shows a range of block sizes from 512b to 8MB in both sequential and random workloads. This chart also shows queue depths between one and 32.
Random data performance is almost universally measured with 4KB blocks at a queue depth of 32. This metric shows what manufacturers want end users to see, though it doesn't accurately reflect real-world performance. We show random performance with 4KB blocks at several queue depths ranging from one to 32 for most devices. PCIe-based products scale well past this queue depth, so we go as high as 128 in some tests.
In each review, we show a comparison between sequential reads and writes at a queue depth of two. We also break random read performance into groups on a bar graph at each queue depth. These random 4KB charts are divided into high and low queue depths.
