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Re: [Xen-users] Re: Performance Issues: I/O Wait

To: <s.seitz@xxxxxxxxxxxx>
Subject: Re: [Xen-users] Re: Performance Issues: I/O Wait
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Wed, 24 Oct 2007 07:30:58 -0600
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I'm not using tg3 cards, but they are Broadcom (Dell PE1950 on-board). 
There is an add-in, dual-port Intel card present, though, so maybe I'll
give that a try.

My "local" disks are also LVM volumes in DOM0 on a hardware RAID1.  I
then present the LVM volume as xvda, xvdb, etc., to the guest and then
partition in the guest.  The iSCSI volume that I'm using for testing is
a software-initiated (open-iscsi) connection inside of DOM0 that's part
of a volume group.  I then created a volume in that group (different
group from volumes from on-board RAID) and presented that to the domU as
xvdb.  I'm using ext3, currently, but XFS is on my list of filesystems
to try.


>>> Stephan Seitz <s.seitz@xxxxxxxxxxxx> 10/24/07 7:17 AM >>>
Nick Couchman schrieb:
> Stephan,
> Thanks for the tips - I'll give them a try.  One clarification - for
> disabling transmission checksums, is that inside the domU or inside
> dom0?

Hi Nick,

I dont' know if it's really necessary, but we're disabling transmission
checksums on every domain including dom0.
Btw. some weeks ago i noticed a thread at the list with problems using
tg3 cards. As we don't own cards with Broadcom Tigon3, i didn't mention.

> Some of the tests was using NFS, but lately I've been testing with
> and even local block devices and it seems to happen on those, too,
> though not to the same degree.

This sounds really strange. We've tried different kinds of domU disks
are currently using dom0 LVM's on locally attached raid arrays. It is
really paranoid, but we avoided disk images with the same filesystem as
the underlaying. so we didn't test ext3 on ext3 or xfs on xfs. Besides
this restriction, we didn't notice any BIG performance problems.



Stephan Seitz
Senior System Administrator

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