[dm-devel] Re: [linux-lvm] Re: [RFC] Multiple Snapshots - Manageability problem

[Dan Kegel]

On Jan 23, 2008 8:16 AM, Tomasz Chmielewski <mangoo at wpkg.org> wrote:
> Vijai Babu Madhavan, Thu, 11 Jan 2007 11:18:13 -0700, wrote:
>
> > The problem of DM snapshots with multiple snapshots have been discussed
> > in the lists quiet a bit (Most recently @
> > https://www.redhat.com/archives/dm-devel/2006-October/msg00034.html).
> >
> > We are currently in the process of building a DM snapshot target that scales
> > well with many snapshots (so that the changed blocks don't get copied to each
> > snapshot). In this process, I would also like to validate an assumption.
>
> Any news on that?
>
> Still, with multiple snapshots write performance degrades linearly - is
> any work done to change that anytime soon?

Yes.  Dan Phillips has implemented a shared snapshot exception store.
You can try it out now if you like; it's at http://zumastor.org.
It feels a bit different from the user's point of view than LVM, though.
It plays well with the device mapper and can be used with any
block device (LVM or non-LVM).
- Dan