high i/o usage

[Stefanita Rares Dumitrescu]

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