Articles: Storage

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Disk Response Time

For 10 minutes IOMeter is sending a stream of requests to read and write 512-byte data blocks with a request queue of 1. The total of requests processed by each HDD is much larger than its cache, so we get a sustained response time that doesn’t depend on the HDD’s buffer size.

This review abounds in surprises! We had hoped that Western Digital’s drives would deliver a good response time at reading but we had not expected such excellent results. The response time of lower than 12 milliseconds is superb for 7200rpm products! Frankly speaking, we don’t even remember easily when we saw such a low response time before. And you should keep it in mind that these HDDs have full-size 500GB platters with over 200,000 tracks each. We want to applaud to Western Digital for such a clever implementation of a composite heads actuator.

Seagate Barracuda XT doesn’t look brilliant in comparison with Western Digital’s as well as other drives. It can only surpass the Caviar Green whereas the Barracuda LP with its 5900rpm has better results. It is unclear for us why the Barracuda XT, having a lower seek latency, delivers a higher response time. Interestingly, the drive shows identical results on both controllers. This again proves the fact that the statistical method of this test helps minimize the influence of secondary factors.

There are no surprises when it comes to writing. We can note the highly effective deferred writing of the Hitachi and the improved deferred writing algorithms in Seagate’s products (the XT is much better than the LP).

Next goes the test of average positioning speed. The drive is being bombarded with read requests like in the response time test, and we calculate the difference between the LBA addresses of the previous and next requests and divide it by the time it took to perform the request. In other words, we have the distance (in gigabytes) the drive can run through in 1 second.

High recording density and fast heads are the two key factors of success in this test. Western Digital’s HDDs have both and easily take two top places. The Seagate XT, probably due to its high response time, gives way to the two power-efficient models. The Hitachi is poor as its recording density is lower than that of the other HDDs. Even its 5-platter design (the number of platters is a certain advantage in this test) can’t save the day.

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