KVM virtual machines and storage.
I currently run a necessary Windows 7 (Home Premium) installation in a
VirtualBox virtual machine on my Debian Unstable desktop. Its OK, but I
have had the occasional glitch when Debian tries to upgrade by kernel
version and for one reason or another the VirtualBox kernel module
hasn't kept up.
I would like to migrate to a KVM setup, where the required module is in
the mainline kernel. I feel that would be safer longer term.
One problem, which I haven't satisfactorily solved so far, is backing up
the files on the disk in that virtual machine. The best I can do is
back up the entire file that represents the disk. However the vast
majority of that disk is not changing on a regular basis and at 120GB of
the image in use, it takes a lot of resource to back it up. I would
much prefer some sort of approach that allows me to copy only the recent
changes to a rolling backup/archive store I have set up for my normal
(linux) desktop .
A possibility that occurred to me is that I could make the disk used by
the virtual machine a raw image file on an LVM logical volume, which I
use the snapshot capability of to take a frozen snapshot of the disk
file at some moment in time. Mount that snapshot on the loopback
device, so that I get to see all the individual files and then back them
up. However I am not sure that would work, as, I presume, the disk
image contains bootsectors and stuff like that. Has anyone used this
sort of approach, and if so how did they get round the issue of device v
filesystem.
The second option maybe something to do with the fact that libvirt can
allocate "chunks" of space out of a LVM volume group, but I haven't been
able to find out any more about how it does this. Do these "chunks"
appear as logical volumes? Can a snapshot of them be taken and mounted
separately as a filesystem?
Any other ideas?
The other area that is currently puzzling me is the migration process.
At the moment the "disk image" that windows 7 is working with contains a
hardware environment that is created by Virtual Box. If I move to KVM I
presume that some of the devices will not be the same. Does Windows
manage with these changes, or would I be better creating an environment
from scratch (including re-installing all my key applications)
--
Alan Chandler
http://www.chandlerfamily.org.uk
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