Re: [Xen-users] Block level domU backup

["Javier Guerra" <javier@xxxxxxxxxxx>]

On Tue, Oct 28, 2008 at 3:22 PM, John Madden <jmadden@xxxxxxxxxxx> wrote:
> On Tuesday 28 October 2008 04:04:39 pm Agent Rooker wrote:
>> But if someone could make clear the dangers and pitfalls associated
>> with this plan, that would be very helpful.
>
> Yeah, pausing a domain does nothing to its disks from the domU's OS's point of
> view.  A pause freezes everything in memory, but commits nothing that's in
> domU's filesystem buffers and whatnot to disk -- the whole point is to not
> disrupt the OS.  If you block-level back up a paused domain, the restored
> filesystem will be corrupted.  Given your existing backup from within the
> domU, I don't believe you're gaining anything here.

the point of pausing the DomU is to get hold of a snapshot of memory
state, as well as the block device(s).  when restoring, the DomU would
return to the 'same' moment it was when paused.  both the disk and CPU
would get back in time.

as mentioned, any dangers would be those related with 'external'
state: network connections, hardware clock, and such.  i'd guess that
a mostly autonomous server should survive this kind of snapshotting,
and go back to work; but if it depends on other systems, losing so
many connections at once might (shoud?) trigger a reboot.  or at least
a service restart.

doesn't sound like something worthy to replace real backups; but might
buy you much lower restore times, if you have the capacity to do both.

-- 
Javier

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