This helped me a great deal. Thanks. I just have a few questions...
1) is it best to unmount the /mnt/lvfoo/ before or after kpartx -d? because you have it in your procedure list both before and after kpartx -d.
2) is it possible to explore this dump file by either mounting it or some other method?
3) what is the best procedure to replace this dump file in case of a disk failure? i.e. just install xen and use virt-install?
4) is this the best possible method of backing up a domU?
Thanks.
Gerd Hoffmann wrote:
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.
Many thanks for this solution, it helps me a lot.
If this can help someone, here are the steps to backup a Domu
(filesystem on LVM in backend and on xvda in frontend) with the dump
command from Dom0 (Fedora 8), using one of the 2 solutions you advised,
kpartx :
----------------------------------------------------------------
# The DomU named "foo" must be stopped before dump
xm shutdown -w foo
# Creates device mapper mappings /dev/mapper/lvfoop[1234] for
/dev/vg00/lvfoo
kpartx -v -a /dev/vg00/lvfoo
# Mounts temporarly the filesystem to backup
mount /dev/mapper/lvfoop1 /mnt/lvfoo/
# Launches the dump
/sbin/dump 0 -L FULL_foo -f /BACKUP-XEN/foo.colddump /mnt/lvfoo/
# Umount the filesystem
umount /mnt/lvfoo/
# Removes the mappings
kpartx -d /dev/vg00/lvfoo
# Unmount the filesystem
umount /mnt/lvfoo
# The DomU can now be restarted
xm create --config /var/lib/xend/....
----------------------------------------------------------------
Regards,
Anne Facq
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