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Re: [Xen-users] Using lvm for domUs

To: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
Subject: Re: [Xen-users] Using lvm for domUs
From: Goswin von Brederlow <brederlo@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 04 May 2007 12:42:25 +0200
Cc: Goswin von Brederlow <brederlo@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Tijl Van den Broeck <subspawn@xxxxxxxxx>
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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.


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