much iowait - how to reduce?

[Igor Sysoev]

On Mon, Jun 16, 2008 at 09:15:44PM +0200, Edo Frederix wrote:

> I am running nginx/0.7.1 on my debian (2.6.24.3 kernel) system. You can see my nginx.conf here: http://pastebin.com/m63c18e1
> 
> My system has much iowait: http://i27.tinypic.com/288crwm.jpg. This is due to some disk activity every 5 seconds. Here are some samples of "vmstat 1":
> 
> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>  0  2      0 3188220  41632  61408    0    0     0  2280 9119 6100  1  4 73 22
>  0  0      0 3187680  41632  61936    0    0     0   272 10516 8027  1  4 93  2
>  0  0      0 3188004  41632  61256    0    0     0     0 9446 6479  1  4 95  0
>  0  0      0 3188052  41632  61216    0    0     0     0 9533 6893  1  3 96  0
>  0  0      0 3187880  41632  62052    0    0     0     0 10639 8117  2  6 93  0
>  0  0      0 3186936  41632  64132    0    0     0     0 9797 6898  1  4 95  0
>  1  1      0 3189304  41636  61324    0    0     0  4692 9052 6414  1  4 65 29
>  0  3      0 3188508  41636  62656    0    0     0  1124 9107 6302  2  4 72 22
>  0  0      0 3187448  41636  63044    0    0     0     0 8601 5591  1  5 87  8
>  0  0      0 3184968  41636  65344    0    0     0     0 10273 7832  2  6 92  0
>  0  0      0 3184900  41636  65024    0    0     0     0 10104 7827  2  5 93  0
>  1  0      0 3181960  41636  68428    0    0     0     0 9675 7242  2  5 93  0
>  0  4      0 3183416  41636  68892    0    0     0  9528 7025 3921  1  2 55 42
>  0  0      0 3186076  41636  63620    0    0     0   440 8508 5839  1  5 60 35
> 
> As you can see in my nginx.conf, I have disabled logging (even error log). I can not determine where my disk is actually writing, but what I do know is that it is related to nginx. When our site gets busy (200mbit traffic), iowait increases. There are no other important processes running on the server.
> 
> My question now is: Is this normal behaviour and how can I reduce the iowait?

If you serve large static content, then this is normal: nginx worker
processes wait on disk reads.


-- 
Igor Sysoev
http://sysoev.ru/en/