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Random Read & Write Patterns

Now we’ll see the dependence between the drives’ performance in random read and write modes on the size of the data block size.

We will discuss the results of the disk subsystems at processing random-address data in two versions. For small-size data chunks we will draw graphs showing the dependence of the amount of operations per second on the data chunk size. For large chunks we will compare performance depending on data-transfer rate in megabytes per second. This approach helps us evaluate the disk subsystem’s performance in two typical scenarios: working with small data chunks is typical for databases. The amount of operations per second is more important than sheer speed then. Working with large data blocks is nearly the same as working with small files, and the traditional measurement of speed in megabytes per second becomes more relevant.

IOMeter: Random Read, operations per second

It is the response time of the drive that is the most important factor when reading in small data chunks. Therefore we’ve got five drives going close to each other, and one slow Seagate. First place goes to Western Digital, but its advantage is negligible.

IOMeter: Random Read, MBps

The Samsung takes the lead when the data chunks are larger. The Seagate doesn’t lose too much here because the speed of sequential operations becomes a factor, too. As a result, the HDDs are overall very close to each other in this test.

IOMeter: Random Write, operations per second

Like at reading, writing in small data blocks depends on the drive’s response time. But as opposed to reading, the resulting speed depends not on how fast the heads are moving around the platters and not on the recording density per platter but on the firmware algorithms, particularly on the depth of deferred writing and on the efficiency of requests reordering. We’ve got two clear leaders here: the drives from Western Digital and Fujitsu. The Seagate is the loser. The speed of the latter drive doesn’t depend much on the size of the data chunk. It is not going to show us any deferred writing at all in IOMeter Database.

IOMeter: Random Write, MBps

It is the sequential speeds of a drive that affect its performance here. As a result, the Western Digital wins this test while the Seagate gets closer to the others.

 
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