[Xen-users] Re: Backup running domUs (was iSCSI Volumes and Xen)

["Nick Couchman" <Nick.Couchman@xxxxxxxxx>]

> How do the so-called 'bare metal recovery' solutions do it on real running
> boxes? - I've always assumed they had some hook into the kernel to force a
> flush of the IO or maybe some scripts for installed daemons.

I imagine it depends on the solution - I'm sure some of them have hooks into 
the kernel to make sure data is flushed to disk before creating a 
snapshot/image, but I also imagine that some of them assume that journaling and 
such will take care of most of the data issues.

> 
> I suppose the only way one can guarantee the snapshot is consistent (yes,
> I know its still only a snapshot) is to actually shutdown the domU
> properly and snapshot the lvm before restarting it?

Maybe, I dunno - Microsoft Windows has VSS, which allows applications to 
register and provides hooks for backup applications and such to interact with 
the system while insuring data integrity.  I'm sure there are other things out 
there that allow for similar functionality, and it would certainly be cool if 
Xen could take advantage of the VSS hooks - perhaps in the GPLPV drivers.  I'm 
not trying to put any more work on James, just throwing the idea out there 
that, at least for Windows machines, VSS integration might actually be a good 
place to start.

-Nick



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