iostat

On Linux, use the iostat command to check if disk I/O is a bottleneck for your database.

We generally find the form:

iostat -xm 2

to work well. (Use a number of seconds with iostat, otherwise it will display stats since server boot, which is not very useful.)

Use the mount command to see what device your /data/db directory resides on.

Fields

• %util - this is the most useful field for a quick check, it indicates what percent of the time the device/drive is in use. If the number if near 100%, your server may be physical disk I/O bound. (There are some volume situations where this statistic overstates, but most often it is correct.)
• r/s - reads per second.
• w/s - writes per second
• rMB/s - read megabytes per second
• wMB/s - write megabytes per second
• avgrq-sz - average request size. The smaller this number, the more random your IO operations are. This is in sectors : typically sectors are 512 bytes, so multiply by 0.5 to see average request size in kilobytes.

On Windows Server use the performance monitor utility.