[Linux-ha-dev] Re: [DRBD-user] drbd peer outdater: higher level implementation?

Lars Ellenberg lars.ellenberg at linbit.com
Mon Sep 15 10:49:15 CEST 2008

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

On Mon, Sep 15, 2008 at 09:59:53AM +0200, Lars Marowsky-Bree wrote:
> On 2008-09-15T08:28:18, Lars Ellenberg <lars.ellenberg at linbit.com> wrote:

> > assume CRM is the only entity promoting/demoting drbd.
> > 
> > would it not be enough for a Primary on connection loss to
> > set some constraint pinning the master role on that node/node group?
> > 
> > the DRBD after-resync handler can then remove that contraint again.
> The idea is interesting. A RA modifying its own constraints ...

well, that is the point. that is what we are talking about the whole
time, constraining the not-up-to-date side to not go live.
why not use the constraint infrastructure for that.

> However, it wouldn't work for a true split-brain. If the primary does
> that before being fenced by the secondary (which, given awkward
> circumstances for the split-brain, is possible), and the partition
> heals, the master would be pinned to the "wrong" node briefly.
> Also, given that it is a split-brain and the constraint is only on one
> side, the secondary would allow itself to be promoted - okay, so the
> cluster never would before the primary has been fenced, but neither
> must the master continue before the secondary has been fenced ...

so it can cause a crm fail (restart) of the other clone,
or preferably (in my opinion) of a dummy resource colocated with the
other clone, if that is needed to cause the other node to be fenced if
if it is reachable, no-brainer.

if you have a true split-brain,
and it in fact happens that both partitions pin their node as only
possible location of the master, then later rejoin, we should have
complementary constraints, causing both diverged datasets to be taken
offline. that is even desirable.

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

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
please don't Cc me, but send to list   --   I'm subscribed

More information about the drbd-user mailing list