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Re: [Xen-users] Backup solution

  • To: 'xen-users' <Xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "Fajar A. Nugraha" <fajar@xxxxxxxxxxxxx>
  • Date: Tue, 10 Jul 2007 08:43:12 +0700
  • Delivery-date: Mon, 09 Jul 2007 18:41:34 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Artur Linhart wrote:
> OK, but - if You create the LVM snapshot volume and make the backup of it,
> You assume the OS running in VM has written everything correctly to the
> logical volume and the logical volume is in consistent state. 
> But this assumption seems to be dangerous for me, especially by Windows DomU
> - how can You be sure, the OS hdd driver has written everything to the
> logical volume before You create the snapshot volume?

In general, you don't.

However, like I said earlier, for production system you'd generally
design a system that
MUST be able to survive a power failure/hard reboot anyway. Part of
doing this is ensuring that applications ALWAYS flush disk cache (with
fsync, etc.) on every write (to transaction logs, datafiles, etc).
Oracle AFAIK does this by default, MySQL can be setup to do so.

As for "the logical volume is in consistent state", when snapshots are
mounted there's an automated journal replay (if you use journaling
filesystem), meaning it should always be in consistent state.

I believe it basically comes down to this : if your domU can survive a
power failure/hard reboot, it should be able to use LVM snapshots for

As others have pointed, this is not the only available backup solution.
You should choose one that fits your need best.



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