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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.

We will discuss the results in two ways. 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.

The speed of the disk subsystem with small data blocks depends only on the response time parameter, so the graphs lie close to each other, the Seagate 15K.1 with its 15,000rpm making the only notable difference.

When the data block size is increased to 128 kilobytes and larger, it is the sequential read speed that becomes important. Therefore the Hitachi C10K300 is successfully competing with the Seagate 15K.1 and even beats the latter on very large data blocks. The old Seagate 10K.1 looks poor against the others due to its low recording density.

Now let’s see what we have at writing.

It is the response time parameter that determines the drives’ results again but we can see a sudden performance hit of the Hitachi C10K147 and a smaller performance hit of the Fujitsu on 128KB data blocks.

The two mentioned products improve on larger data blocks, though. They take what places they deserve with their sequential write speed. The Hitachi C10K300 is first again as it has the highest-density platters. Take note that the high sequential speed (due to its high spindle speed) of the Seagate 15K.1 allows this drive to keep in second place despite high response and low recording density.

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