HD Tach will test the sequential read, random access and interface burst speeds of your attached storage device (hard drive, flash drive, removable drive, etc). All drive technologies such as SCSI, IDE/ATA, 1394, USB, SATA and RAID are supported. Test results from HD Tach can be used to confirm manufacturer specs, analyze your system for proper performance, and compare your performance with others. HD Tach is very easy to use, quick, and presents data in easy to read graphs, including the ability to compare two storage devices on screen at the same time for easy analysis.
Bursts are provided only for your review. SSD's don't cache the same way HDD's do (in many cases they don't cache reads at all), so burst testing typically results in figures that are lower than the sequential throughput figures.
SandForce controllers have always been a bit tricky in playing nicely with HDTach. The way it accesses the device under test makes some HDDesque assumptions, but here it seems to translate to a fine-grained curve in lookup / access times. The curve seen above (and below) is a combination of two factors at play:
- At lower capacities, the controller is effectively slower as it has fewer flash dies on tap to communicate with (meaning each die pulls extra duty).
- At higher capacities, the controller has a larger number of LBAs to track, and therefore lookups take slightly longer.
The latter is a weakness for SandForce, but mainly only in single threaded operations, which HDTach is known to be.
HDTach feeds the tested drive a continuous string of small sequential read requests. This is a single threaded operation, which means the SSD doesn't get to see what's coming next. The lower the QD=1 latency of the controller pipeline, the better the numbers we see from this test. It doesn't equate to real-world maximum throughput, but it does mean something for analysis, which is why we include these results.
The same 'sweet spot' at around 120GB can be seen above, but remember, this is only due to a benchmark-specific interaction that is unlikely to be replicated in real-world usage. Better sequential figures are present on the next page (HDTune).