On Tue, Apr 28, 2009 at 6:51 PM, Antoine Benkemoun
> The dom0 is a pretty minimal install of Debian with nothing else then Xen,
> SSH and fail2ban running. It can easily fit on 256MB of RAM. In fact, it
> averagely uses 100MB of RAM.
Hmm, interesting. I should test Debian or Ubuntu for firewall domUs sometimes.
> I have reproduced the problem by generating IOs with 3 torrents and 1 file
> XM top shows :
> commun ------ 2959 3.5 262144 12.7 262144
> 12.7 1 1 1828352 1567395 3 16267 3411443 1848929 32
> Domain-0 -----r 2617 2.7 262240 12.7 no limit
> n/a 1 0 0 0 0 0 0 0 32
Since you ommit the headers, the output is quite confusing :P
What are vbd stats for the domU, does it have lots of reads/writes?
> Load average for "commun", the domain being loaded, is above 5. Memory is
> only used at about 50% and only 440k of swap is used. Along goes the usual
> symptoms, really slow web page loads and really slow reactivity of about
> everything in the domain. Reactivity in the other domains is rather normal.
So it's not swap problem. However looking at your previous iostat
output %util is over 99 (which means your disk is busy), r/s over 180,
and rsec/s almost 8000 (meaning about 4 MB/s). Based on this numbers
I'm GUESSING you only have one lowend disk (not raid), and it has
reached its IOPS caps. In other words, get more disks :P
A suggestion, it would probably be easier to manage if you use LVM and
put dom0 and domU each on its own LV. That way iostat can show per-LV
staticstic so you can easily determine who's using most disk I/O.
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