How to find out which processes are causing a
hard disk I/O overhead in GNU/Linux
To find out which programs are causing the most read/write overhead
on a Linux server one can use
iotop
Here is the description of
iotop - simple top-like I/O
monitor, taken from its manpage.
iotop does precisely the same as the classic linux
top but for hard disk IN/OUT operations.
To check the overhead caused by some daemon on the system or some
random processes launching
iotop without any arguments is
enough;
debian:~# iotop
The main overview of iostat statistics, are the:
Total DISK READ: xx.xx MB/s | Total DISK WRITE: xx.xx
K/s
If launching iotop, shows a huge numbers and the server is facing
performance drop downs, its a symptom for hdd i/o overheads.
iotop is available for Debian and Ubuntu as a standard
package part of the distros repositories. On RHEL based Linuxes
unfortunately, its not available as RPM.
While talking about keeping an eye on hard disk utilization and
disk i/o's as bottleneck and a possible pitfall to cause a server
performance down, it's worthy to mention about another really great
tool, which I use on every single server I administrate. For all
those unfamiliar I'm talking about
dstat
dstat is a -
versatile tool for generating system
resource statistics as the description on top of the manual
states. dstat is great for people who want to have iostat, vmstat
and ifstat in one single program.
dstat is nowdays available on most Linux distributions ready
to be installed from the respective distro package manager. I've
used it and I can confirm tt is installable via a deb/rpm package
on Fedora, CentOS, Debian and Ubuntu linuces.
Here is how the tool in action looks like:
The most interesting things from all the dstat cmd output are
read, writ and
recv, send , they give a good general
overview on hard drive performance and if tracked can reveal if the
hdd disk/writes are a bottleneck to create server performance
issues.
Another handy tool in tracking hdd i/o problems is
iostat
its a tool however more suitable for the hard core admins as the
tool statistics output is not easily readable.