Re: [Xen-users] Re: 100% safe way to backup domU: (was Yet another backup)

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Mark Williamson wrote:
> >  Is there a way to get a complete image out of an LVM? The only way I found
> > to extract files from an LVM snapshot was to mount it, but when you do that
> > you are mounting a badly corrupted file system, and trying to take backup
> > from it.
> >     
> I think you should just be able to backup the device file that you'd usually 
> mount.  Just treat the snapshot's device file as *the* file to backup.
>   
Unfortunately, backing up devices is rife with risks, due to databases 
(which may have things in RAM not yet written to disk but which will 
mess up things that *have* been written to disk if they don't happen), 
and due to disk paging (stuff that to a user looks like it's been 
written to disk may not have actually made it to the disk yet, it may 
not be paged out yet). The sync command helps with the latter, but can't 
do anything about the former.
Thinking about these things is why people who make industrial grade 
backup software get paid.

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