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Re: [Xen-users] Xen VMs on GFS volumes

To: Michael Mey <michael.mey@xxxxxx>
Subject: Re: [Xen-users] Xen VMs on GFS volumes
From: Anders Bruun Olsen <anders@xxxxxxxxxxxxxxx>
Date: Mon, 12 Dec 2005 10:59:35 +0100
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On Fri, Dec 09, 2005 at 10:29:07AM +0100, Michael Mey wrote:
> > > Again, my setup is with an iscsi storage box (an IBM DS300) which both
> > > machines has access to. If I don't run a clustering filesystem and mount
> > > the same device on both machines, I run into trouble (obviously). But I
> > > am not sure if a partition containing a VM actually needs to be mounted
> > > two places at the same time, or if it just really quickly unmounts on
> > > the first dom0 and mounts it on the second?
> > Forgot to mention that I am using Xen 3.0.0.
> theoretically, GFS would work in the case that you have a clustered 
> filesystem ,accessible from your two dom0s, and you store the file-backed 
> VBDs of your domUs on it, so you don't need cluster-awareness within your 
> domUs.
> Unfortunately, GFS doesn't support, AFAIK, r/w mount of files on GFS over the 
> loopback-device, which Xen uses to make the VBDs accessible for the domUs.
> If you tried to start a domU with that setup, you would get lots of i/o 
> errors 
> within your domUs. There's a thread on this list about that and I made the 
> same experience.
> Maybe OCFS2 would do a better job at this point.

I tried OCFS2 earlier, but could not get it to work, the nodes in the
cluster could not see each other. But that's off-topic here :)

> Using partitions of your iscsi box as VBDs for domUs should work fine 
> considering live migrations. You don't have to use a cluster filesystem, just 
> use e.g. ext3 on a LV of your iscsi-box, put the domU root fs on it, make 
> sure you have access to it from both your dom0s, be sure to not have mounted 
> it from somewhere and start your domUs.
> I have a setup running with Xen 3.0 (testing, release of Monday which you can 
> get from the website), the VBDs stored on LVs over fibre channel in my san, 
> and migration works nice. For testing purposes I just run a test, domU is 
> busy with i/o tests etc., and was migrated approx 400 times in the last 20 
> hours - still running :)

Thanks to all who answered, I now have it working (except I haven't been
able to test out live migration yet because of limitations at my end,
but I am sure it will work nicely) with CLVMD and reiserfs.

After getting a domU up and running with a Gentoo stage3 in it, I get
the following error when it checks the root fs during boot:
get_dma_info failed Bad file descriptor
I have mapped the LV to hda1 because sda1 just gave an error. Anything
that can be fixed or should I just ignore it?

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