[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:
http://thread.gmane.org/gmane.linux.lvm.general/9898/focus=9899

A bit later, someone actually did the re-implementation of that concept in C:
http://thread.gmane.org/gmane.linux.lvm.general/10886

"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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