Here are some commands to monitor and identify Disk I/O related server loads.

iostat

iostat give stats about disk i/o usage. Some of the important values are

* %iowait = if this value is higher, your server is waiting on IO. This can be due to high disk operation on your server or disk is faulty.

* %idle = it is better to have higher value. If your disk usage is higher, the value goes down.

# iostat
Linux 3.10.0-514.26.2.el7.x86_64 (server1.hostonnet.com)    Monday 17 July 2017     _x86_64_    (8 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.53    0.00    0.11    0.51    0.00   98.85

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda              20.62       422.52       102.49   12530308    3039304
sdb               0.00         0.03         0.00        914          0

#

Here we have 2 disks in the server. Only one of them is n use. Since Disk I/O is mainly bottle neck most servers face, it is better to use both disk, this way I/O load get distributed between 2 disks. For this, you may move MySQL data folder to 2nd disk.