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Database Patterns

In the Database pattern the tested 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 the IOMeter: Database pattern.

We will build diagrams to illustrate each drive’s performance at different request queue depths.

This is all quite illustrative, especially due to the peculiar behavior of the Samsung hard disk drive. It slows down when connected via USB 2.0, losing nearly all of deferred writing and hardly showing any read request reordering. It is only at a request queue depth of 16 that you can see some notable performance growth.

Vantec’s USB 3.0 implementation looks better and shows a more considerable increase in performance at long queue depths. However, the graph for a queue depth of 4 requests is still almost the same as the graph for a queue depth of 1 request. The Buffalo’s USB 3.0 produces zigzagging graphs. If it were a SATA-connected HDD, we’d say that its firmware is poor. The enclosure’s controller seems to be trying to help the HDD at long queue depths as much as it can, but does not do that consistently. There is one thing that doesn’t change with this enclosure, though. There is almost no difference in its performance at short queue depths.

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