[DRBD-user] Heartbeat & DRBD.SplitBrain.Auto recovering

Lars Ellenberg lars.ellenberg at linbit.com
Mon Nov 24 16:17:22 CET 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 Wed, Nov 19, 2008 at 05:37:30PM +0100, Francisco José Méndez Cirera wrote:
> I have the following config now:
> after-sb-0p discard-younger-primary
> after-sb-2p violently-as0
> If DRBD finds two primaries after SplitBrain, it should discard the changes on
> younger primary node and starts sync.
> However, nothing happens, and I have to solve the split brain manually. Nodes
> lose communication forever..(WFConnection and Standalone)
> How can I resolve Split Brain automatically? I want that the primary younger
> node discards changes after both nodes can communicate in order to replicate
> all the modificsations, once the split brain is solved , automatically!

please be aware that a node in Primary role should never become sync target,
because of cache coherency issues (the block device being modified
underneath the cache by the resync process).

so to effectively automatically recover after a split brain,
you'd need to make sure that the to-become-synctarget node
is in secondary role.

if it is not, you can trigger the "pri-lost-after-sb" handler,
which is supposed to reboot the node, which normally should
get it up as Secondary.

So for the NOT recommended way of automatically recovering after split
brain, throwing away all transactions done on one of the nodes,

doing something along the lines of:
  after-sb-0pri discard-least-changes;
  after-sb-1pri call-pri-lost-after-sb;
  after-sb-2pri call-pri-lost-after-sb;

while having a handler
  pri-lost-after-sb "echo b > /proc/sysrq-trigger; reboot -f"

might do what you ask for.

but are you sure you want to
throw away transactions
everytime you experience a network hickup?

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

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