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Re: [Xen-users] increase size for dom guest using lvm online

To: Simon Hobson <linux@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] increase size for dom guest using lvm online
From: "Thaddeus J. Hogan" <thaddeus@xxxxxxxxxx>
Date: Tue, 18 Aug 2009 10:54:47 -0500
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At the moment, I believe the size passed to the guest is fixed at creating time, so if you enlarge the volume, the guest won't get to know about it until it is shut down and re-created.
I just verified that this is the case on Xen 3.2 on Debian 5. I was not able to get the guest to pick up the change in device size.

There is the option of doing LVM in the guest, though this will make the volumes more difficult to access from the Xen dom0. If you do lvm in the guest you will be able to attach a new chunk of disk, then run pvcreate on it and add it to a volume group in your guest. However if the dom0 is running lvm as well it will try to register the volume groups defined by the PVs that you are intending to map through to your guests. You have two options for preventing this from creating problems on the dom0. First, you could exclude from the scan process in lvm.conf those devices destined to be used with LVM in a guest, but you will not be able to mount these volumes in the dom0 as a result. The other option is to name your volume groups differently for every guest so there are no conflicts when lvm in the dom0 does a pvscan, this allows you to use the volumes from dom0 but can be a manageability issue.

Personally I don't think the tradeoffs are worth it for online resize. I do my LVM on the dom0 and then send individual LVs to the guests as xvda, xvdb, etc. but I cannot resize these without a reboot.

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