[Lustre-discuss] e2scan MDT back-up

[Daire Byrne]

Brian,

----- "Brian J. Murrell" <Brian.Murrell at Sun.COM> wrote:

> On Wed, 2009-03-04 at 17:03 +0000, Daire Byrne wrote:
> > 
> > Once you move to LVM then you can snapshot the MDT and mount that without
> > unmounting the production MDT. You should probably destroy the snapshot
> > afterwards as it affects performance somewhat.
> 
> And just to be absolutely clear for those who don't realize, as the
> number of snapshots of a single device increases so does the
> performance penalty.
> 
> There is another snapshot technology at http://zumastor.org/ that
> claims to efficiently store snapshots to as not to suffer the same problems. 
> I have yet to find the time to evaluate it though.

I looked at zumastor. Although it didn't get any slower with extra snapshots
it took quite a hit (~ x6 drop in writes) with just a single snapshot. It was
also a bit buggy and I didn't particularly like the userspace<->kernel interface.
Far more promising is the port of zumastor exceptions to the kernel and the work
being done to add a generic shared exception store interface to device-mapper 
(and ultimately LVM):

  https://www.redhat.com/archives/dm-devel/2009-February/msg00014.html

It is a Redhat effort so it might actually be useful one day.

Daire