HD Tach is a physical performance hard drive test that uses a special kernel mode VXD to get maximum accuracy by bypassing the file system.
The HD Tach sequential read test is a little bit different from other benchmarks. Most benchmarks create a file on the hard drive and test within that file. The problem is that modern hard drives use a zone bit recording technique that allows different read speeds depending on where the data is located. Data on the outside of the drive is much faster than data recorded on the inside.
With this test we NEVER reach advertised speeds, so please don't worry about that. It is the nature of the test. That said, HD-Tach does not respond well to the RAID0 setup as you can see.
When we look at write performance we see slightly slower scaling, we still get 205 MB/sec in this test, and that's okay for this drive. But not what we'd expect.
In addition to sequential read performance, HD Tach tests the drive's random access time. Random access is the true measure of seek speed. Many drives advertise sub 10 millisecond seek speeds, but seek speeds are misleading. Also again, without a physical head that needs moving around, the SSDs are just so fast as they have no mechanical moving parts. Here obviously ... the smaller number is better, 0.1 ms.
As you can see, read write performance in not at all constant, while it should be. We can't explain it really (click to enlarge screenshot btw).
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