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Re: [Xen-users] Backup domU image at runtime

Andrea Monti wrote:

I think that taking a backup of a virtual disk while it is used is even worse: if you yank the power cord and you are using a journaled file system, the file system will probably recover by itself. If you backup a virtual disk while it is used you are taking an inconsistent image of the journal and an inconsistent (corrupted) image of the files!

If you do a "file copy" then yes, the whole thing will be inconsistent. If you use something like an LVM snapshot then it would be a "point in time" copy and equivalent to yanking the power cord.

I think that the risk will always be high: you cannot be guaranteed that no process will write any file during the backup

See above about snapshots.

and you have no way to check if the backup is working (the os will see the filesystem as ok, but application data could still be corrupted)

Indeed. Which is why I specifically said it depends heavily on what the guest is doing. Databases in particular would be a problem as most DB engines do a lot of their own caching.

Simplest advice on such backups is ... DON'T !
Less simple is ... DON'T unless you understand the nuances enough to determine that it's safe for **your** situation.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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