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Re: [Xen-users] Xen and I/O Intensive Loads

To: "John Madden" <jmadden@xxxxxxxxxxx>
Subject: Re: [Xen-users] Xen and I/O Intensive Loads
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Wed, 26 Aug 2009 11:41:55 -0600
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What filesystem did you use for this test in the domU for the e-mail storage?  I'm currently running XFS on my volume where the GroupWise data sits, and I'm wondering if the filesystem isn't tuned properly.  Could you give me a run-down of what filesystem you used, and what parameters you used for creating the filesystem (block size, inode size, etc.)?



>>> On 2009/08/26 at 11:32, John Madden <jmadden@xxxxxxxxxxx> wrote:

> I'm attempting to run an e-mail server on Xen.  The e-mail system is
> Novell GroupWise, and it serves about 250 users.  The disk volume for
> the e-mail is on my SAN, and I've attached the FC LUN to my Xen host,
> then used the "phy:/dev..." method to forward the disk through to the
> domU.  I'm running into an issue with high I/O wait on the box (~250%)
> and large load averages (20-40 for the 1/5/15 minute average).  I was
> wondering if anyone has ideas on tuning the domU to handle this - is
> there a better way to forward the disk device through, should I try
> using an iSCSI software initiator in the domU, or is it just a bad
> idea to put an I/O load like this in a domU?  Unfortunately mapping
> the entire F/C card through to the domU isn't really an option - the
> FC card accesses other SAN volumes for the Xen host, so it needs to be
> present in dom0.

If this turns out to be a global issue, I'd certainly like to hear about
it.  I recently load-tested a postfix+cyrus domU with 6 SATA-backed
spools and 6 FC-backed meta partitions for about 300,000 IMAP accounts
and consistently delivered around 100 messages/sec to them.  That load
was obviously all i/o-bound, but at what I'd consider to be an
acceptable delivery rate (which seems to be the most
performance-challenging operation at least with Cyrus).  I did see
similar load averages though.

This was with a RHEL 5 domU and a CentOS 5 dom0 and phy: mappings. 


John Madden
Sr UNIX Systems Engineer
Ivy Tech Community College of Indiana

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