On Tue, Oct 28, 2008 at 3:34 PM, Javier Guerra <javier@xxxxxxxxxxx> wrote:
> 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
>
That's what I'm thinking, anyway. As I said in a previous message in
this thread, "...we're also doing domU level backups with NetBackup."
So in case my plan totally backfires, we're no worse off than we would
be otherwise. If we do end up needing to reboot the domU after
restoring it on the other xen server, that's still a lot faster than
rebuilding the server and then restoring from the tape files.
We have proper backups going at a different time each night as well,
this is really more to reduce the downtime we would face in the case
of a hardware failure with the xen-server. We should really be using
a network area storage cluster and a HA xen cluster to provide the
best availability and reliability, but until I can convince the
department to expense for that, this will have to do for now.
An alternative solution would be to bring the domUs down for a cold
block-level backup each night, but that is just a little more downtime
than I would like.
--
Agent Rooker
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