Re: [Xen-users] High IOWAIT

[Nick Anderson <nick@xxxxxxxxxxxx>]

Lorenzo Milesi wrote:
> Hi
>
> I've a setup with opensource xen3.0.3 on debian etch.
> lately i'm experiencing problems with the main debian domu, which runs
> samba cyrus apache and few other services.
> i'm having very high machine load due to iowait at 100%. i suppose the
> culprit to be cyrus, but i'm not sure. i have 4.5g mail, split in
> something like 100000 files. I already remounted my partition with
> noatime,nodiratime as suggested by the cyrus site, but didn't help. The
> vm has only 1 virtual disk of 100gb, 70% free, on lvm.
> is there anything xen could be involved in?
I would guess its imap thats causing your problem. What kind of disk 
back end is the vm on? I know you said lvm but is that lvm on a hardware 
raid, software raid, if so how many disks and what raid level?
Ive had a web/mail server in the past that iowait was just tearing up 
performance. I migrated imap mail off to a different machine and that 
made a *huge* difference. That was just a single disked server with no 
hardware or software raid.
I know people have said don't run a database or email in a vm but it 
seems to me all that needs to be addressed is having a fast storage back 
end. I hope I am right, as I plan to migrate our database and mail 
servers to virtual machines. Initially they will be on the same piece of 
hardware but eventually they will on separate dom0s. I know in the 
meantime there will be some IO contention but I am hoping that I can 
mitigate some of that with relatively fast IO back end and a lot of RAM.

--
Nick Anderson <nick@xxxxxxxxxxxx>
http://www.cmdln.org
http://www.anders0n.net

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