John Haxby wrote:
Mathieu Kretchner wrote:
I'm sure it's a frequent question asked a lot of time, But is it
possible to backup domU without stopping it ?
Else could you please give me some url talking about the subject ?
Yes, it's possible. You need to suspend it (xm save) copy the file
system image(s) and the memory image and then xm restore it. If you're
using an LVM-backed virtual disk then you can take a snapshot of the
logical volume so that the guest isn't down for long.
This allows you to restart the guest operating system at exactly the
same point that it was stopped. This sounds good, but any network
connections (for example) that were present when the system was saved
will be long gone by the time the system comes back up. If one of these
connections, for example, was a message being sent by sendmail then the
message will be resent which will result in the lucky recipient
receiving a second copy, possibly days, weeks or months after the original.
If you just want the file system image then what you've done is the same
as pulling the plug on a live system and copying the raw disk: you'll
need to replay journals or run fsck or both and, of course, unless the
applications on the systems take especial care to avoid re-running
transactions that were previously completed elsewhere you'll have
trouble. Again.
So yes, it's possible, but you almost certainly have to have the
cooperation of the guest in order to make such a backup.
I think I heard of someone backing up their virtual system without
losing existing network connexions. Or maybe they migrated it between
real systems.
It's starting the backup-up system where one might have interesting
problems such as continuing to write to files that were open for writing
when the backup was taken.
--
Cheers
John
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