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xen-users
Re: [Xen-users] High IOWAIT
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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