When it comes Disk performance, DISK I/O plays an important role. 

To Find out and Monitoring Linux Disk I/O:

Login into your server through ssh using putty, Just like TOP Command in Linux which used to monitor load on the server we have IOTOP command to monitor I/O of Disk. 

You should get a list of running processes along with information about their current disk I/O usage. 

The output will look something like this: