Re: [linux-lvm] Enterprise Backup Software with good support for LVM

[David Brown <lvm@davidb.org>]

On Tue, Nov 29, 2005 at 01:43:17PM -0500, Steffen Plotner wrote:

> I would like to add that creating backups of LVM snapshots is sensible,
> as the data is in a crash-consistent state. Today's operating systems
> can definitely handle this type of state. I have developed scripts that
> effectively netcat contents from LVM snapshots to a remote machine
> (either into another logical volume or simply a file). 

If you are using a journalling filesystem, then the snapshot should be
consistent.  XFS and LVM2 work together to try and make the snapshot even
more consistent.

The question, then would be can you integrate the LVM2 snapshot
creation/removal with the backup software.  I backup my snapshot volumes
using custom backup software (file based) and things work fine.

I have discovered a minor problem with snapshots, but haven't figured out
exactly what is happening.  It seems that with some types of databases,
modifications made to the database happen across the snapshots (happen to
both images).  I suspect it has something to do with mmapping a file, but I
can't reproduce it with my own code.  For my instances, the changes don't
hurt anything, since they are databases that are essentially caches of
other derrived information, but a real database file could be a problem.

Dave