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Multithreaded Read & Write Patterns

The multithreaded tests simulate a situation when there are one to four clients accessing the hard disk at the same time – the clients’ address zones do not overlap. We will discuss diagrams for a request queue of 1 as the most illustrative ones. When the queue is 2 or more requests long, the speed doesn’t depend much on the number of applications. You can also click the following links for the full results:

Well, the increased distance between the data threads proves to be a serious difficulty for most of the tested HDDs. Three models from Western Digital are ahead irrespective of the number of data threads: the two old BEVT series drives and the new 750GB model. The fourth drive from Western Digital has much more modest results in every case despite the seemingly similar firmware.

The HDDs from Samsung and Hitachi are good at two threads, but the Hitachi team give up the fight at three threads. The Seagate drives wake up and leave all the others behind, save for the three leaders, when processing four data threads.

Some people argue that high performance of a particular drive may be due to its dedicating most of its resources to one data thread while ignoring the others. We measured the speed of each thread and show it in the diagrams: each thread is colored a different shade. As you can see, sometimes the leading HDDs indeed choose one data thread as the main one. Sometimes but not always. When there are a different number of threads, the same model may distribute the total speed evenly among them. And if you also consider the distribution of speed among the threads at requests queue depths other than 1, you will find no regularities at all (you have to believe us as we won’t publish such a huge table here).

There are no dramatic performance hits at multithreaded writing because the large amounts of cache memory and deferred writing algorithms of modern HDDs help smooth out the negative aspects of multithreaded load. We can see three leaders clear enough: the Hitachi 7K500, the 750GB BPVT series drive from WD and the Samsung M7E.

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