Our PCI-Express SSD tests are conducted with a Core i5 processor on an ASRock Z97 Extreme6 motherboard. This is one of the few motherboards that is fully capable of providing the bandwidth for the M.2 SSDs regardless of its Z97 chipset. Tests are run in a Windows 8 environment and even if the native tests were conducted in Windows 10, the resulting performance should be the same.
We use Iometer to determine the random read and write speeds with 4 kB data blocks. The performance with small data blocks is very important, because in Windows (and other operating systems) 4 kB is the most commonly used block size for hard disks and SSDs. We run the tests with a queue depth of 1, 2, 4, 8, 16 and 32. This queue depth indicates how many simultaneous instructions are sent to the SSD. The performance at low queue depths is very important for consumer applications, and with QD32 SSDs can show off what they're capable of.
Iometer also measures the read and write speed with 1 MB data blocks. We use QD32, but here the number of parallel requests matters very little since the SSD controller is very good at distributing these over multiple SSD channels.
We also simulate the access patterns of a file server and a database server with Iometer. The database test consists entirely of random 8 kB operations, 67 percent of which is reading, and 33 percent is writing. The file server test is 80 percent reading and 20 percent writing, with the following transfer sizes: 10% 512 bytes, 5% 1 kB, 5% 2 kB, 60% 4 kB, 2% 8 kB, 4% 16 kB, 4% 32 kB and 10% 64 kB. Both the file server test and the database test are done with queue depth 1, 2, 4, 8, 16 and 32.
All Iometer tests are conducted with completely random data, so that SSD controllers using compression tricks don't have an edge. Each test runs for at least 30 seconds, which is much longer than comparable tests in the various benchmark tools.
The popular AS SSD benchmark also tests performance with 4 kB data blocks (QD1 and QD64) and the sequential read and write performance. The advantage of running a test that is similar to Iometer is that AS SSD converts the scores to a total score that provides a good impression of the general performance of an SSD. Secondly, AS SSD is easy to install on your own computer which allows you to compare scores.
Real-world benchmarks: PCMark
For consumer applications, the real-world benchmark PCMark8 is much more important. PCMark8 uses traces from the Windows 8 period: Adobe Photoshop, Adobe Illustrator, Adobe Indesign, Adobe After Effects, Microsoft Word, Microsoft Excel, Microsoft PowerPoint, World of Warcraft and Battlefield 3.
Continuous activity test
We conduct two continuous activity tests in which we run a workload for 30 minutes on the SSD and measure the average performance for each minute. First, we do this with the Iometer 4kB random write test, and the the Iometer database simulation. Both continuous activity tests are done with QD32 and a file that takes up 75 percent of the available flash memory. For normal consumer use these results aren't very important, but for professional applications - in servers for example - these scores are essential, more so than any other benchmark results.
Consistency refers to how much the SSDs performance may fluctuate from one second to the next. In order to measure consistency, we run an Iometer 4kB random write QD32 workload once again, but rather than taking a snapshot of the drive's performance each minute, we record an average for each second. Admittedly, performance consistency is mainly something that is relevant for the enterprise market. Those who put an SSD in a heavy-duty database server will want to be sure that the performance of the used storage is predictable, as big ups and downs may result in erratic behaviour for certain workloads. For consumer workloads, performance consistency matters very little, although it will certainly influence the performance of SSDs when putting them in RAID 0. After all, when using a RAID 0 array, blocks of data will be written to two or more disks, which means that the slowest drive (the "weakest link") will determine the overall level of performance. When one of the drives has poor performance consistency, the overall performance of a RAID 0 array will be relatively low, seeing as how the odds of one of the two drives having a performance "dip" are relatively high.