high i/o usage
pchychi at gmail.com
Mon Oct 5 11:21:39 MSD 2009
On Mon, Oct 5, 2009 at 12:02 AM, Stefanita Rares Dumitrescu
<katmai at keptprivate.com> wrote:
> hi guys,
> i am using centos 5, nginx version: nginx/0.8.16
> , and php-fpm and i have switched to nginx on one of my very busy servers.
> however, i see very high i/o usage, and the site works pretty sloppy.
> below is my iostat and df output. as you can see i get around 25 mb/s
> written at any time.
> mysql is on a second drive, and there is pretty much nothing else. however i
> cannot understand why the i/o is so high. i expect that maybe because of log
> writing, but i checked the log folder, and it's not.
> I have setup in the beginnging the worker processes to 8, but for some
> unknown reason after 1 2 minutes, nginx stops, so i had to increase it to
> 64, and now it stays up. but i have left the i/o thing, which i cannot make
> anything out of it.
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 123.88 0.00 25.94 0 52
> sda1 0.00 0.00 0.00 0 0
> sda2 0.00 0.00 0.00 0 0
> sda3 1.00 0.00 0.02 0 0
> sda4 122.89 0.00 25.92 0 52
> sdb 15.42 0.07 0.00 0 0
> sdb1 15.42 0.07 0.00 0 0
> sdc 69.15 0.58 1.27 1 2
> sdc1 69.15 0.58 1.27 1 2
> root at rum [/usr/local/nginx/logs]# df -h
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda4 331G 50G 265G 16% /
> /dev/sda3 15G 1.2G 13G 9% /tmp
> /dev/sda1 99M 18M 77M 19% /boot
> tmpfs 7.9G 0 7.9G 0% /dev/shm
> /dev/sdb1 367G 60G 289G 18% /home2
> /dev/sdc1 58G 13G 43G 23% /home3
This is a known issue with cent os 5.*, its the HD read/write method
used as default (though i believe that 5.* has major issues)
You will experience the same issue with any utility or tool that write
to disk (try using 'wget' to download a file to disk .. then use wget
to write to /dev/null 'wget -S http://site.com/file -O /dev/null'
you will see the issue. I would also recommend using "dstat" to
diagnose the problem as it will provide you with live data, something
like what you have posted above only you can monitor entire system
i/o,network,cpu resource utilization.
id recommend moving off of centOS (debain/gentoo or a better os,
ubuntu) or perhaps downgrading to 4.*
Payam Tarverdyan Chychi
Network Security Specialist / Network Engineer
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