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Re: [Xen-users] Using lvm for domUs

To: Goswin von Brederlow <brederlo@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Using lvm for domUs
From: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
Date: Fri, 04 May 2007 11:47:16 +0100
Cc: xen-users@xxxxxxxxxxxxxxxxxxx, Tijl Van den Broeck <subspawn@xxxxxxxxx>
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Goswin von Brederlow wrote:
Nico Kadel-Garcia <nkadel@xxxxxxxxx> writes:

Goswin von Brederlow wrote:
If you have enough disks/partitions you can make one VG per domU and
share that for dom0 and domU using cluster lvm (clvm) to keep them in
sync. Instead of real disks/partitions you can run lvm in dom0, create
a LV per domU and run lvm on it again. But then you have to
specifically include the first lvm LVs in lvm.conf and run vgscan
twice. I think that should work.

Have you tried this? For various reasons, I'm looking at using iscsi
or clvm for having commong storage and permitting live migrations, and
for snapshotting the LVM's for backup purposes. (LVM snapshots and
rsnapshot, a combination made in heaven!)

I was thinking about drbd0.8 active-active with clvm but drbd0.8
caused crashes. And drbd0.7 can't do active-active.

But with iscsi and clvm there should be no problem. clvm is just a
little daemon that basically runs vgscan on all hosts whenever you
change something.

We use lvm inside LVs here on a HA cluster but the inside lvm is
exclusively for the domU. No sharing with dom0. The dom0 lvm is so we
can resize and create/destroy LVs on the fly, the inside lvm is
because all our servers are setup the same.

Unfortunately for me, my Dom0 hardware does not have the CPU's for
full virtualization, so access to backup media has to go through Dom0
or be pushed over the network. And the network or Xen usage seems to
double my backup timef, so I *need* Dom0 to be able to access the hard
drive contents of DomU.

You can always create LVs in dom0 and export them as sda1/2/3/... to
domU. You have to reboot domU to resize anyway. That way you can then
snapshot them in dom0, mount the snapshot and run your backup.
I do that now, but I can't do a raw install that way using virt-install or virt-manager, so doing that virst install is a pain in the neck to get a working image. The jailtime.org images are good, but not so useful for non-RPM based OS's.

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