[dm-devel] change tracking with block-level granularity using md

[Joe Thornber]

On Wed, Dec 18, 2013 at 09:04:17AM +0100, Thomas Knauth wrote:
> Hello list,
> 
> I am the author of the following paper
> 
> https://www.usenix.org/conference/lisa13/technical-sessions/papers/knauth

I've been working on a similar problem.  There's a new target called
dm-era taking shape here:

https://github.com/jthornber/linux-2.6/blob/era/drivers/md/dm-era-target.c

It uses bloom filters to track changed blocks.  Userland tools will
access snapshots of the metadata via a metadata snapshot.  I expect to
post the finished code to dm-devel some time in Jan.

More information about what I'm trying to do can be found here:

http://device-mapper.org/blog/2013/11/12/retaining-cache-coherency-with-external-snapshots/


BTW: If you're using dm-thin your backup scenario is trivial.  Just
take a snapshot of the volumes you want to back up.  Take a metadata
snap.  Examine the metadata to see which blocks have changed since you
last backed up.  Copy data.  All you need is already written.

- Joe