random read disk stress test

When a GNU/Linux machine exhibits a high iowait (i.e. more than 20% of the processor time is locked waiting for IO to complete), it does not always mean a lot of bytes are read or written. It is demonstrated that reading randomly on the disk will create conditions in which less than 5Mb/s are read and the disk will be busy most of the time, which translates into an iowait greater than 20%. A workaround is to give more RAM to the (virtual) machine so that pages read are cached in memory and read only once, therefore reducing the probability of random reads.
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