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Database Pattern

In the Database pattern the disk array is processing a stream of requests to read and write 8KB random-address data blocks. The ratio of read to write requests is changing from 0% to 100% throughout the test while the request queue size varies from 1 to 256.

You can view tables with the results by the following links:

We’ll discuss the results for queue depths of 1, 16 and 256.

The HDDs deliver similar performance in a RAID0 array at low loads. The WD4000YS and Hitachi T7K500 are somewhat better than the others when the percentage of writes is high. The Samsung T166S is on the losing side, except at high percentages of writes. It is working in the quiet mode after all. The Seagate is very slow at writing.

The participating HDDs split up under the higher load. Both drives from Western Digital go ahead, the newer WD4000ABYS copying with write requests better. The Hitachi is trying to compete with the leaders but has a slump at 80% writes. There seem to be some flaws in its firmware. Samsung’s three disks are roughly similar to each other, the quiet HD403LJ being as fast as the others and even somewhat faster at reading. The Seagate is good at reading but slows down at writing.

The HDDs behave in the same way under the highest load. Western Digital is in the lead, followed by the Hitachi that still has a slump in the middle of the diagram. The Seagate is good at reading and rather slow at writing.

The HDDs differ more in RAID10 arrays even under low load. WD’s drives are in the lead again, but their graphs begin to fluctuate somewhat at high percentage of writes. As a result, they are eventually outperformed by the Hitachi. Samsung’s HDDs behave differently: the HD400LJ performs write requests slower than the HD401LJ which has a larger cache buffer. The “quiet” HD403LJ is predictably slow at high percentages of reads and accelerates at high percentages of writes but has some fluctuations in performance. The Seagate is good at reading and rather slow at writing, again.

Most of the HDDs speed up at reading when we increase the load. We’ve got the same leaders, though: both drives from Western Digital and the Hitachi. The differences between the firmware versions can be seen easily. The WD4000ABYS is faster than its mate at writing whereas Samsung’s 16MB-buffer drives are equals, leaving their 8MB counterpart far behind. The latter’s performance is somewhat surprising: it looks like its firmware has lost all of its NCQ algorithms.

Western Digital enjoys a larger advantage under the highest load. This brand’s HDDs cope better than the others with the most difficult case when there is the same amount of reads and writes. Again, the Samsung HD400LJ is rather slow at high percentages of reads. Can its cache be entirely dedicated to deferred writing? These are very odd results. We rechecked them but to the same effect. This is obviously a firmware flaw.

Every HDD shows performance fluctuations at certain combinations of reads and writes when working in a RAID5 array. However, Western Digital’s disks are still in the lead while the Samsung T166S takes last place as it has done under low loads in the other arrays. Interestingly, the Hitachi cannot compete with the leaders at high percentages of writes as it did in the other types of arrays.

The graphs smooth out under higher load. WD’s drives enjoy a big lead over the others. Talking about the losers, the Samsung HDDs are worse at reading while the Hitachi is worse at writing. The Hitachi seems to dislike working in a RAID5.

There is nothing new under the highest load. It’s the same as at a queue depth of 16 requests.

 
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