[DRBD-user] use drbd on wan: ho to merge a snapshot without snapshot merge support

Lars Ellenberg lars.ellenberg at linbit.com
Thu Sep 22 11:41:17 CEST 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Thu, Sep 22, 2011 at 11:09:41AM +0200, Lionel Sausin wrote:
> Le 21/09/2011 21:05, Mia Lueng a écrit :
> > Hi Sausin:
> >
> > Thanks for ur advice.
> >
> > Now we use the script to create LVM snapshot before each
> > synchronization. If the sync process is failed(primary is down or net
> > link is broken) , then recovery the secondary node from the previous
> > snapshot immediately.
> > But the lvm snapshot merge is only supported in rhel6,(we uset sles11
> > sp1).  Is there another way to merge the snapshot?
> None that I know of, sorry. In that situation I would probably replace
> the failed node ASAP and dd the snapshot over the network.
> Lionel.

Just so you know it is theoretically possible:

If you do not have a kernel with snapshot merge support,
you still can do an "offline snapshot merge", if you are careful.

Back in 2008, I explained how, and why, this can work:

A bit later, someone actually did the re-implementation of that concept in C:

"Use at your own risk and apply own mental effort as appropriate",
as mentioned in the original post...

If you have the space available,
maybe rather dd the snapshot to a new device.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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