Maybe - depends on how the disks are configured. Is this just a "standard" PC with IO busses on the motherboard ?. Or are you using iSCSI, fibre channel, something else ... ?No, it doesn't - it means the system is idle, and there is uncompleted I/O still oustanding. Subtle but important difference. Have a read of this, it seems a reasonable explanation.iotop works like top, but for I/O - however it show what processes are doing the most I/O, not which files are being hit. I/O is done by disk (sector) address - I know of no easy way to do the "reverse lookup" to work out the file(s) involved.

As suggested, collectl gives finer data, and also has history on a per-process basis, so you can do analysis for bad periods in the past.

Another tool of interest may by latencytop, but CentOS may not have the required kernel options enabled for that to work.

Well, it means the system is blocking a task while waiting for I/O of some kind to complete. More than anything, in a system that is experiencing performance issues, where %iowait is constantly high, it's a sign that there might be a technical issue (bug, config issue, maxed-out performance, inefficiency, or just lots of work being performed) with a given raid array or controller.

CentOS should be able to run collectl; as we use it on RHEL all the time.

I meant options for latencytop - Fedora for example doesn't have them. I have amended my post above.

collectl is perl that simply relies on /proc and /sys (last I looked), and certainly should run on almost any modern system.