Yet another awesome top clone for Linux, this time to make monitoring disk I/O simple: iostat. This post over at MDLog has a great introduction and explanation. For me it was available with apt-get, as iostat. Then you just run iostat. It produces a readable top-like display of what processes are currently performing the most disk I/O:
Here I have the display sorted on disk read activity, but any of the columns can be used as the sorting reference by pressing the left and right arrows. This tool could be quite useful in combination with mtop and other tools to see if, for instance, a MySQL instance is performing too much I/O, or if queries are still using memory efficiently.
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Definitely that’s a step in the right direction.
Unfortunately it’s still hard to tell who’s wasting most disk IO in too many situations.
Suppose you have two processes – dd and mysqld.
dd is doing massive linear IO and its throughput is 10MB/s. Let’s say dd reads from a slow USB drive and it’s limited to 10MB/s because of the slow reads from the USB.
At the same time MySQL is doing a lot of very small but random IO. A modern SATA 7200 rpm disk drive is only capable of about 90 IO operations per second (IOPS).
So ultimately most of the disk time would be occupied by the mysqld. Still iotop would show dd as the bigger IO user.
– Teodor Milkov