See Your Disk IO with iostat

A handy tool that is not installed by default on Red Hat / CentOS is iostat. If your application is chugging, and the processor or network isn't maxed out, disk IO may be the bottle-neck. iostat is part of the sysstat package, so go ahead and install it:

# yum -y install sysstat

Run iostat to see your input / output statistics:

# iostat 5 5