Re: [Xen-users] restoring files to guest domains

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

Jared wrote:
> From what I've read of LVM, v2 includes read/write support.  So, I'd 
> think that I could do the following and it'd just work:
> lvcreate -L 50G -s -n guest-backup /dev/vg1/guest-disk
> mount -t ext3 -o rw /dev/vg1/guest-backup /mnt/snapshot
> cp /mnt/backup/guest/etc/fstab /mnt/snapshot/etc/fstab.restore
> umount /mnt/snapshot/
> lvremove -f /dev/vg1/guest-backup
Dude, it doesn't work that way.
The way I see it, you're writing data to /dev/vg1/guest-backup, but then 
you REMOVE the LV afterwards. And you expect it to show up on 
/dev/vg1/guest-disk?
> Like I said, I must either be really dense or I'm just 
> misunderstanding the meaning of "read/write" here, because the file is 
> certainly not being written as I'd expect.
The "read/write" part means you (should) be able to create a snapshot of 
an LV, and write new data to that snapshot. The data will then be 
available ONLY to the snapshot, not to the original LV.
To accomplish what you're looking for, you must copy the file using 
either scp (or some other network-file-transfer), or shutdown the guest 
and mount the LV on dom0.
This is different from (lets say) Solaris Zones, where a non-global zone 
filesystem is visible from the global zone. In this case you can write 
files from the global zone and have the non-global zone see the new 
data. I believe it's not recommended to do so, but it works, since both 
global and none global zone can have simultaneous access to the same 
filesystem. It won't work with Xen.
If you absolutely must have the "feature" above, you might want to look 
at solaris and brandZ zones. Basically it allows you to run some linux 
distros on top of solaris kernel, giving global zone and brandZ zone 
access to the same filesystem.
Regards,

Fajar

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