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Database Patterns

In the Database pattern the drive 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% with a step of 10% throughout the test while the request queue depth varies from 1 to 256.

You can click this link to view the tabled results for IOMeter: Database pattern.

We will build diagrams for request queue depths of 1, 16 and 256.

Things are quite interesting at the minimum queue depth. The Western Digital RE4-GP is ahead of the other HDDs both at reading (thanks to its quick heads) and writing (thanks to its huge cache). The other graphs are close to each other except that the Samsung is slow at writing and the Western Digital AV-GP and the 1.5TB Caviar Green are slow at reading. And while the results of the AV-GP can be explained by its slow heads, we don’t know what happens to the 1.5TB Caviar Green at pure random reading.

When the queue depth is increased to 16 requests, we have some more surprises. The WD RE4-GP is still beyond competition at writing, but loses its leadership at reading. It is slower at reading than the Seagate HDDs that have higher spindle rotation speed as well as than the 2TB Caviar Green. The 1.5TB Caviar Green is again the worst drive at reading but the Samsung is the overall worst throughout all request queue depths.

The competition gets tougher at high loads. The Western Digital RE4-GP is unrivalled at writing, but finds itself the slowest of all at reading. The Seagate 7200.11 wins at reading, followed by the WD Caviar Green series in which the 1.5TB model goes ahead at pure reading. The Samsung does not like server loads and fails this test.

Winding up this part of our tests, we will build diagrams showing the performance of each HDD at five different queue depths. 

The Samsung EcoGreen F2 resembles the desktop F1 DT series with its weak NCQ and modest deferred writing. It also has the specific behavior at high percentages of reads that makes us suspect that its heads are deliberately slowed down.

The Seagate HDDs have everything a decent HDD must have. And it is good that the Barracuda LP at 5900rpm is about as fast as the Barracuda 7200.11. However, the power-efficient model has occasional performance slumps under medium queue depths, so its firmware needs improvement in terms of request reordering.

Western Digital’s Caviar Green drives behave in the same manner, except that the 1.5TB model is slower at pure reading at any queue depth. This must be a feature of its firmware whether intentional or not.

The Western Digital AV-GP is similar to the other HDDs from the same company but behaves in a calmer manner. It has very modest deferred writing and weak NCQ.

And finally, the RE4-GP differs greatly from the other HDDs. It boasts superb deferred writing: it can really put those 64 megabytes of cache memory to good use. However, it has no request reordering whatsoever. This is actually no problem for an HDD which is designed for RAID arrays because the RAID controller can take care of request reordering and the lack of NCQ in the HDD even helps avoid potential conflicts. However, it is rather odd to see an NCQ-less drive in the year of 2009. This is the reason why it is slower than the others at every request queue depth save for the minimum one.

 
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