iotop and iostat

[Trevor]

Two tools that can help detect disk performance problems:
- iotop
- iostat

The top and vmstat commands will both provide information on I/O - I/O wait time.
However, the iotop command helps us identify the processes doing I/O operations.

Another something to consider is what disks are being used in these I/O operations - this is where the iostat command comes into play.

To check the I/O statistics in detail, the iotop and iostat commands can be used. These two commands are used to identify performance problems with storage devices, including local disks, or the network file system.

iotop is similar to the top command, but it shows the disk activity in real time. This utility (iotop) looks at the kernel I/O usage information and displays a table of the
current I/O usage, through processes or threads, on the system. It also shows the
bandwidth, and the read and write I/O time, of each process or thread.

Note: A nice little option that can be used with the iotop command is -oo (or --only). These options check which processes are actually using disk I/O - and only those
processes will be displayed. This can come in real handy when you've got a lot of
processes running on a system, and you want to be able to focus only on the ones
that are actually using disk I/O - this is your ticket to achieve that output!

The command iostat is used to monitor the load of the input/output device of the
system, looking at how long devices are active in relation to their average transfer
rates. It can also be used to compare activity between disks.

The iostat command generates reports that can be used to change the system
configuration to better balance the input/output load between the physical disks.
The iostat command generates two types of reports:
1) CPU utilization and
2)  use of the device

Lets look at just a couple of options that can be used with the iostat command:

#  iostat -d
If we add the -d option to the iostat command, we can view I / O statistics just for the
storage devices no CPU utilization info:

#  iostat -p
On the other hand, if we add the -p option to the iostat command, we will show I / O statistics of all devices and their partitions.

#  iostat -x
If you really want to fill your plate with information, with a view of detailed I/O
statistics for all devices, add the -x option to the iostat command:

Got disk performance concerns?  Make use of these two tools as a starter for
your interrogation!!!