Xen users - Mar 2007 - mount xen partitions inside logical volume from dom0?

I''ve installed a FC5 domU under RHEL5-beta2 dom0 with virt-manager.

As the disk for domU I used:

phy:/dev/mapper/VolGroup00-LogVol02,xvda,w

In the domU I have partitions:

/dev/xvda1 on / type ext3 (rw)
/dev/xvda2 on /var type ext3 (rw)

How do I access these partitions from dom0? For example if I take an
LVM snapshot of
LogVol02, how do I mount the / partition of the domU installed on the
volume for backup purposes?

Regards,
Peter

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Peter Peltonen wrote:
> I''ve installed a FC5 domU under RHEL5-beta2 dom0 with
virt-manager.
>
> As the disk for domU I used:
>
> phy:/dev/mapper/VolGroup00-LogVol02,xvda,w
>
> In the domU I have partitions:
>
> /dev/xvda1 on / type ext3 (rw)
> /dev/xvda2 on /var type ext3 (rw)
>
> How do I access these partitions from dom0? For example if I take an
> LVM snapshot of
> LogVol02, how do I mount the / partition of the domU installed on the
> volume for backup purposes?
You use the "lomount" command, I believe. Type "lomount
--help" to gain
access to the partitions inside :/dev/mapper/VolGroup00-LogVol02. 


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On 3/11/07, Nico Kadel-Garcia <nkadel@gmail.com>
wrote:
> You use the "lomount" command, I believe. Type "lomount
--help" to gain
> access to the partitions inside :/dev/mapper/VolGroup00-LogVol02.
But I thought lomount can handle only disk images? At least that''s
what the help says:

# lomount -h
Usage: lomount [-verbose] [OPTIONS] -diskimage FILE -partition NUM [OPTIONS]
All OPTIONS are passed through to ''mount''.
ex. lomount -t fs-type -diskimage hda.img -partition 1 /mnt

And I am talking about partitions made by the FC6 Anaconda installer
to the logical
volume.

After reading the RHEL5/FC6 Xen documentation through again I realised I must
use kpartx:

kpartx -av /dev/VolGroup00/LogVol02

and then I can mount the partition:

mkdir /mnt/LogVol02p1
mount /dev/mapper/LogVol02p1 /mnt/LogVol02p1

Of course the domU must be shutdown to do this and one has to umount the
partition before starting the domU again. But now I can do the following:

- pause the virtual machine
- take an lvm snapshot
- unpause the virtual machine
- mount the snapshot volume
- backup the snapshot volume
- delete the snapshot

Now I''m just wondering what''s the best way to backup the
snapshot...

Cheers,
Peter

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On Sun, Mar 11, 2007 at 05:35:38PM +0200, Peter Peltonen
wrote:
> On 3/11/07, Nico Kadel-Garcia <nkadel@gmail.com> wrote:
> >You use the "lomount" command, I believe. Type "lomount
--help" to gain
> >access to the partitions inside :/dev/mapper/VolGroup00-LogVol02.
> 
> But I thought lomount can handle only disk images? At least that''s
> what the help says:
> 
> # lomount -h
> Usage: lomount [-verbose] [OPTIONS] -diskimage FILE -partition NUM
[OPTIONS]
> All OPTIONS are passed through to ''mount''.
> ex. lomount -t fs-type -diskimage hda.img -partition 1 /mnt
> 
> And I am talking about partitions made by the FC6 Anaconda installer
> to the logical
> volume.
> 
Are these like magical partitions - unlike say the terribly normal ones
you get with "fdisk /dev/VolGroup00/LogVol01"? :-)

Nico''s right, lomount works just fine. You might want to try it out
before you delete your snapshot:

    lomount -verbose -t ext3 -partition 2  \
        -diskimage /dev/mapper/VolGroup00-LogVol02 /mnt  
    
> After reading the RHEL5/FC6 Xen documentation through again I realised I 
> must
> use kpartx:
> 
Oops!

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