Random Read/Write Patterns

Now that we’ve begun to talk about writing, we’ll run our traditional average response time test.

Like in IOMeter, the Deskstar 7K1000 is the slowest of all Hitachi drives in terms of average read access but performs much better at writing. The ratio of read access time to write access time is indicative of how efficiently disk requests are accumulated and reordered in deferred writing mode. As opposed to our earlier reviews, the efficiency is calculated in percent rather than as a relative coefficient. It shows how much deferred writing reduces the average sector access time.

It is the newest 7K1000 that boasts the highest efficiency, yet it isn’t far better than the Deskstar 7K250. It means there have been no fundamental improvements in the deferred writing implementation despite the introduction of NCQ.

Talking about IBM’s heritage, Hitachi only disabled Tagged Command Queuing in its T7K250 and later models and this technology worked even in the Deskstar 7K400, which was equipped with the modernized electronics from Infineon. And TCQ worked poorly, much worse than in the Deskstar 7K250 even! There was no optimization at reading. At writing the command buffering on the HDD would conflict with deferred writing, resulting in a performance hit in many tests. Surprisingly, the Deskstar 7K400 with a Serial ATA interface, which is also benchmarked with enabled TCQ, does not suffer much. However, its lower speed in many tests is obviously due to TCQ.