System monitoring is an important part of network
administration. Fortunately, there are numerous tools on the market that monitor
performance, network activity, and SMART status of hard drives. One tool that isn’t
very well known is called iostat, and it monitors I/O
(Input/Output) performance related to disk drives.

Some Linux distributions ship with iostat.
If your distribution doesn’t include it, simply download
the iostat source code
and build it as follows:

$ tar xvzf iostat-2.2.tar.gzcd iostat-2.2make

When the build is complete, you’ll have the tool iostat and the manpage iostat.8
in the current directory. To install iostat and its manpage in the /usr/local
directory tree, simply perform a “make install”:

$ tar xvzf iostat-2.2.tar.gzcd iostat-2.2make install

You can run iostat with a number
of options and two optional arguments: “interval” and “count.”
To view disk activity over time, provide it with an interval of 15 (seconds)
and a count of 10 (samples). Here’s how:

$ ./iostat 15 10

However, this will give you only basic information on the
installed physical disk drives. To obtain more information, pass iostat a few more options, such as printing statistics per
disk (-d), printing CPU activity stats (-c), including per-partition stats
(-p), and including extended statistics (-x). For a good sampling of data, enter
this code snippet:

$ ./iostat -Dpxc

Since iostat prints out a lot of
information, you’ll want to keep the manpage handy so
that you can identify what each column means. Some of the information includes
total transfer rate per second, total number of requests per second, number of
reads (and writes) per second, percentage of CPU time spent in user, system,
and idle modes, and much more.

If your system is slowing down and you’re having a hard time
finding the bottleneck, iostat may clue you in on
some problem areas. Even before that slowdown, iostat
can tell you what disks are over- and under-utilized, which allows you to plan
ahead and balance the I/O load.

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