> I am wondering, whether it's possible to migrate a DomU from one XEN Host
> to another *without* using shared storage. All HowTos that I found so far,
> are using some kind of shared filesystem or block device.
Well, as others have said, basically you need the block device the guest is
using to be available at the destination host by the time it gets there...
As others have also noted, that doesn't necessarily mean any horribly crazy
shared cluster thingy.
I guess there's 3 things you might want and it's worth clarifying which:
1) The /entire contents/ of the VBD moves to be stored on the new machine, the
old storage can be discarded.
2) When the domU is on its "home" host it can access the block device using
the normal front<->back connection with high performance. Some simple remote
access setup is used when it's migrated to a foreign host; but not using one
of the very complex shared storage solutions out there.
3) You just don't want to use a complex shared storage solution like a SAN,
iSCSI or something performance-sapping like files on NFS (which is often bad
practice anyhow, under Xen)
For 1 there's not currently a particularly easy solution. The closest is
probably DRBD, since that avoids copying huge amounts of disk space across
during the migration! DRBD has been used with Xen before, some people have
had good experiences with it. You could always ask the DRBD mailing lists
what the status of the multiple-primary support is and whether people have
had success using it with Xen, if you want to check this option out.
Number 2 could be done by hacking up a new, slightly more intelligent, block
device setup script that would either use a local blkback if available or go
to a network server if not.
Number 3 could be done quite simply by running an enbd server to serve disk
images, then putting something like (if memory serves correctly):
disk = ['enbd:server:port, sda1, w']
in the config file. The control tools should automatically connect to the
ENBD server correctly, including setting up a connection during a live
migration. This should be quite simple to set up; you might want to test and
see if the performance is OK for you.
> In case, migrating this DomU won't work, I would have to copy the VM
> manually. Is it possible to access the contents of /dev/sda1 from Dom0?
> Simply shutting down the DomU and mounting /dev/sda1 in Dom0 does not work.
As noted by another responder, simply mounting this won't work because it's a
whole disk image and not a filesystem image.
I'll just reiterate at this point that one should never ever mount the FS of a
running (or currently paused / saved!) domU - preferably not even read-only.
The safest way to mount a domU's filesystem is to make sure the domU is shut
down cleanly first. I expect you're aware of it, but it's worth
emphasising ;-)
Cheers,
Mark
--
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)
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