much iowait - how to reduce?

[Edo Frederix]

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?

Thanks, Edo.
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