[Gllug] what is causing disk activity ?

[Luke Dudney]

On 20/11/08 13:21, Alain Williams wrote:
> On Thu, Nov 20, 2008 at 12:53:07PM +0000, Luke Dudney wrote:
>
>   
>> All of that output refers to stats since boot. For real-time info try 
>> "iostat -x 5" and wait 5 seconds for the second lot of output
>>     
>
> Errrm: I said that I had removed the first block of iostat output. No matter.
>
>   
My bad, I misunderstood.
>> First thing to check would be to see if any processes are blocking on IO:
>>
>> while true; do ps auwx |awk '$8 ~ /D/'; sleep 1; done
>>     
>
> That was interesting. I ran that & walked away for 5 minutes. sda & sdb are SATA disks
> that are mirrored (raid 1) providing md1. mdadm shows no problem with it and
> nagios would have told me if there was a problem.
>
> I must confess to not understanding how the kernel raid works; is it perhaps writing
> status blocks back to disk ?
>
> # while true; do ps auwx |awk '$8 ~ /D/'; sleep 1; done
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> ups       3426  0.0  0.0  37820   684 ?        Ds   Nov17   0:02 //bin/usbhid-ups -a mintups
> root      1908  0.0  0.0      0     0 ?        D<   Nov17   0:51 [kjournald]
> root      4008  0.0  0.0  10188   660 ?        D    Nov17   0:25 hald-addon-storage: polling /dev/hda
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       477  0.0  0.0      0     0 ?        D<   Nov17   0:04 [kjournald]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root      1889  0.0  0.0      0     0 ?        D<   Nov17   0:00 [kjournald]
> exim      6432  0.3  1.3 168364 55080 ?        D    09:46   0:38 spamd child
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root      4008  0.0  0.0  10188   660 ?        D    Nov17   0:25 hald-addon-storage: polling /dev/hda
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root      1884  0.0  0.0      0     0 ?        D<   Nov17   0:00 [kjournald]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root       470  0.0  0.0      0     0 ?        D<   Nov17   2:12 [md1_raid1]
> root      4008  0.0  0.0  10188   660 ?        D    Nov17   0:25 hald-addon-storage: polling /dev/hda
>
>   
Having not used it I'm not sure how the kernel raid works either; it may 
be expected behaviour for those raid1 kernel threads to sit there 
blocking the whole time without actually doing much.

Could your exim + spamassin be the culprit? Is there much happening in 
the mail logs?

Cheers
Luke
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