Xen: mount Windows domU residing on LV under Linux Mint dom0

[powerhouse]

This is for Xen users who run a Xen hypervisor and Linux Mint as dom0 and have a Windows virtual machine installed as domU on a LVM formatted partition.

LVM or logical volume manager is the recommended way of installing domUs onto a partition. I've written another how-to on installing Linux Mint 13 root and /home partitions onto LVs.

Once you have successfully created the Windows domU and installed Windows, you can also access the Windows file system from your Linux Mint dom0.

Warning: Don't mount your Windows domU under Linux in read-write mode while Windows is running - it may cause data loss

It's strongly advised to shut down the guest system BEFORE mounting it under dom0 as shown below !

Install kpartx:

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sudo apt-get install kpartx

List the partitions:

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sudo fdisk -l

The interesting part of fdisk -l is:
Device Boot Start End Blocks Id System
/dev/mapper/lm13-win7p1 * 2048 206847 102400 7 HPFS/NTFS/exFAT
/dev/mapper/lm13-win7p2 206848 125827071 62810112 7 HPFS/NTFS/exFAT


win7p1 is the boot partition, win7p2 is the actual Windows partition which I'm going to mount. lm13 is the volume group I created when installing my Linux Mint system.

Use kpartx to map the new LVs:

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sudo kpartx -av /dev/mapper/lm13-win7

Note: I didn't try /lm13-win7p2 which may also work.

Create a mount point:

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sudo mkdir /mnt/win7 # or wherever you want to mount your Windows partition

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ls /dev/mapper

gives me something like this:
control lm13-root lm13-win7p1 vol1-lm13_backup vol2-swap
lm13-home lm13-win7 lm13-win7p2 vol2-data

lm13-win7p2 is what I want.

Let's mount the Windows file system as NTFS, read-only:

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sudo mount -t ntfs -o ro /dev/mapper/lm13-win7p2 /mnt/win7

And check:

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ls /mnt/win7

Documents and Settings PerfLogs Recovery Users
hiberfil.sys ProgramData $Recycle.Bin Windows
NVIDIA Program Files System Volume Information
pagefile.sys Program Files (x86) temp

Note: Never mount the Windows domU file system under dom0 when it is up and running, unless in read-only mode..

Important: When you're done with the Windows partition,you must remove the partitions with kpartx -d:

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sudo kpartx -dv /dev/mapper/lm13-win7

That was easy.

[powerhouse]

It might be worth noting that kpartx also works perfectly with .img files. I did a snapshot backup of my Windows 7 domU using the script below:

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#!/bin/sh
mv /media/tmp_stripe/lm13-win7.img /media/tmp_stripe/lm13-win7.img.old
lvcreate --size 10G --snapshot -n win7-snap /dev/lm13/win7
echo Creating backup copy of win7...
pv /dev/lm13/win7-snap | dd of=/media/tmp_stripe/lm13-win7.img
lvremove -f /dev/lm13/win7-snap
echo Finished

Notes:
1. /media/tmp_stripe/lm13-win7.img is the Windows 7 .img file (a backup of my virtual Xen Windows 7 "c:" drive).
2. /dev/lm13/win7 is the logical volume containing my Windows 7 installation under Xen: lm13 is the volume group; win7 the logical volume.
3. win7-snap is the snapshot partition of the win7 LV, which is used for backup. I gave it 10GB which is far more than you ever need, unless you create or change files in excess of 10GB during the backup. It actually only holds the changes to the files/file system while backing up, until the snapshot is deleted (removed).
4. "pv /dev/lm13/win7-snap | dd of=/media/tmp_stripe/lm13-win7.img" is the same as "dd if=/dev/lm13/win7-snap of=/media/tmp_stripe/lm13-win7.img", but gives a progress bar and ETA so you know how long to wait.

Now I can mount the .img file as a loop file with kpartx as follows:

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kpartx -av /media/tmp_stripe/lm13-win7.img

Watch the output of the above command.

To access the files, however, there are two more steps required. First we create a folder to mount the loop file in /mnt/win7:

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mkdir /mnt/win7

and then mount the Windows 7 partition:

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mount -t ntfs -o ro /dev/mapper/loop0p2 /mnt/win7

Now you got read access to the files in the .img backup file of a Xen Windows 7 domU. Of course this works as well with any other Xen domU virtual machine. Just adopt the mount -t ntfs to mount -t ext2 or whatever.

To close everything, do the following:

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umount /mnt/win7
kpartx -dv /media/tmp_stripe/lm13-win7.img

Again, adapt to your needs.