[rsyslog] Syslog logging taking too much disk write?

Scott Baker bakers at web-ster.com
Thu Dec 20 18:04:33 CET 2007


I have a semi busy syslog server which logs about 40 or 50 lines per
second. I noticed using dstat that it's taking a TON of disk write.
In the megaBYTES per second range. This seems extremely high to me
so I wrote a script to test it.

http://www.perturb.org/code/log_lines.pl

First download dstat, gkrellm, or iostat and look at what your
normal disk write is per second. On my underused desktop it hovers
around zero or maybe 25KB/s per second.

If I run my script and tell it to log 10 lines to syslog per second

perl log_lines.pl 10

the write usage spikes up to ~160KB/s. We're only writing about 740
bytes of data per second so why is the disk write so high?

If I tell my script to instead log to a local file in /tmp at 10
lines per second

perl log_lines.pl 10 -t

The write usage spikes to ~120KB/s about once every 5 seconds (as
the buffer fills up). I'm curious why syslog writing is so much more
intense? It seems to me on a really busy syslog server that you
could seriously smoke your HDs with all the writing it's doing. Am I
missing something?

-- 
Scott Baker - Canby Telcom
RHCE - System Administrator - 503.266.8253



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