[Fedora-xen] How to backup a Domu filesystem (on LVM) from Dom0 on Fedora 8 ?

[Gerd Hoffmann]

Anne Facq wrote:
> Because in Dom0 the device for a paravirt Domu (/dev/vg00/lvfoo in my
> case) is mapped to a virtual disk /dev/xvda (I created the Domu with
> virt-install), and the only way I found to mount this Domu filesystem,
> is to :
> - get the size of the boot sector of /dev/vg00/lvfoo
>     (with fdisk -ul /dev/vg00/lvfoo)
>     = 63
> - compute the offset (multiply by block size)
> - specify this offset to the mount command :
> mount -o offset=32256 /dev/vg00/lvfoo /mnt/

Uh, oh, quite complicated and error prone.  Can be done much easier.

Option (1): Use kpartx, it will create device mapper mappings for your
partitions.  Try "kpartx -v -a /dev/vg00/lvfoo", should give you
/dev/vg00/lvfoop[1234].  "kpartx -d ... " removes the mappings.

Option (2): (works only with xen kernel): Configure the device as
virtual disk *in Domain-0*: "xm block-attach 0 phy:/dev/vg00/lvfoo xvda
w".  Gives you /dev/xvda[1234].  "xm block-detach ..." removes it.

HTH,
  Gerd