Re: [Xen-users] Xen backups using LVM Snapshots

[Kevin Fox <Kevin.Fox@xxxxxxx>]

On Fri, 2008-10-17 at 10:41 -0700, Javier Guerra wrote:
> On Fri, Oct 17, 2008 at 12:29 PM, Kevin Fox <Kevin.Fox@xxxxxxx> wrote:
> > If you were running a single OS with lvm snapshots (IE, no xen),
> would
> > the snapshots be consistent? IE, no fsck needed ever for the
> snapshots?
> > If so, then there must be a mechanism for LVM snapshotting to tell
> the
> > file system to coalesce to disk before the snapshot.
> 
> No.

Strange that the file system and LVM have enough knowledge of each other
to do online resizing, but not snapshotting.

Guess it wouldn't be easy to implement then.

Kevin


> the snapshots ARE consistent.  consistent to a point in time where it
> was mounted and running.  if do an LVM snapshot, and a VM snapshot,
> you could recreate the running state.
> 
> the difference between a mounted and an unmounted volume is totally
> filesystem dependent; it's not the job of a blockdevice layer.  (this
> is one reason why some people like the "manage everything at
> filesystem" approach of ZFS).
> 
> that 'coalescing' you refer have two parts: a full sync(), and
> unmounting itself.  you can do sync() just before doing the snapshot,
> so the fsck needed when mounting it would be 'almost' guaranteed to
> find it clean.  On journalling filesystems, the metadata, at least is
> fairly safe.  And, on ext3 with data=journal, the files data is just
> as safe.  Other FSs have similar settings.
> 
> --
> Javier
> 
> 


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users