Diagnosing High I/O Wait

• when you see high I/O wait, one of the first things you should check is whether the machine is using a lot of swap. since the hard drive is slower than ram, when a system runs out of ram and starts using swap, the performance will suffer.

• anything that wants to access the server has to compete with the swap for disk I/O.

• it can be difficult to figure out exactly which process is using the I/O, but if you have multiple partitions on the server you can narrow it down by figuring out which partition most of the I/O is on by using iostat.