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, regardless of controller used.
HDTach feeds the tested drive a continuous string of small sequential 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. Here we can see how the various controllers handle this type of workload:
- Marvell (top 4) sees limited read speed, as each IO request in series requires an LBA map table lookup, which is forced to occur in series, slowing the read speed overall. Not shown on the graph is that the read speeds were ~450 MB/sec on the first pass (before the drive was fully written). Writes at QD=1 are handled well, but we see the natural falloff as die count / capacity decreases.
- SandForce (SX900), despite its compression, has always had a problem with QD=1 operations due to the overall high latency of its data pipeline.
- The Samsung 840 Pro's triple core ARM controller does well with very low latency.
- Intel's new 8-channel controller, lifted from their enterprise line, achieves extremely low latency and does very well in this type of test.
This is the sort of reason why we keep these benches around. Their output still has meaning, and when interpreted correctly, can tell us things other benches have a hard time replicating.