Re: [Xen-users] About tape drive.

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Mark Williamson wrote:
> > Save yourself some grief. If the tape drive is being used to write image
> > files, or even directory backups, to a tape drive, you can play some
> > games after the DomU is running to make its internal partitions
> > mountable in Dom0 in read-only mode and do the backup from there.
> >     
> Hmmmm.  I generally don't recommend mounting filesystems of running domUs in 
> dom0, even in read-only form: it can confuse the filesystem driver in dom0, 
> potentially leading (in the worst case) to system instability, corrupted data 
> being read for the backup, etc.  I imagine there are also potential security 
> implications (e.g. privileged data ending up in unprivileged files) for the 
> guest's filesystem.
>   
Oh, that's what LVM snapshots are for! To protect the active filesystem 
from anything the Dom0 might do while mounting the LVM snapshot.
> Backing up the disk image of a running guest is not ideal either, because it 
> will certainly be in an inconsistent state and need fsck to attempt to repair 
> the damage if you want to mount / boot it in future.  The same corruption / 
> security problems apply here too, but it shouldn't make dom0 or domU unstable 
> at the time of the backup.
>   
See above.
> It's best to backup disk images of cleanly shutdown guests.  Or you could 
> backup the disk of a guest which has been xm save-ed *and* back up the 
> guest's memory image at the same time.  The two together contain all the 
> information needed to consistently read the disk when the guest is resumed, 
> although the disk image can't be mounted on it's own (and, if you do, you 
> won't be able to safely resume the guest afterwards!).
>   
"Cleanly shutting down guests" is begging to cause issues for systems 
without high availability, especially databases.
> For tape backups of files within the guest, I generally recommend using a 
> network based backup program, as if you had another physical host.  It's not 
> optimal but it's simple and avoids some nasty tripups / complexities involved 
> in trying to do anything cleverer.
> Cheers,
> Mark
>
>   
If you're going that route, I recommend "rsnapshot" or plain old 
"rsync". If you're clever, you can do it to the LVM snapshot and speed 
the heck out of the process, because most of the files are already there!
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users