[ClusterLabs] Question about two level STONITH/fencing

[Andrei Borzenkov]

On Thu, Feb 5, 2026 at 2:07 PM Klaus Wenninger <kwenning at redhat.com> wrote:
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> On Wed, Feb 4, 2026 at 4:36 PM Anton Gavriliuk via Users <users at clusterlabs.org> wrote:
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>> Hello
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>> There is two-node (HPE DL345 Gen12 servers) shared-nothing DRBD-based sync (Protocol C) replication, distributed active/standby pacemaker storage metro-cluster. The distributed active/standby pacemaker storage metro-cluster configured with qdevice, heuristics (parallel fping) and fencing - fence_ipmilan and diskless sbd (hpwdt, /dev/watchdog). All cluster resources are configured to always run together on the same node.
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>> The two storage cluster nodes and qdevice running on Rocky Linux 10.1
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>> Pacemaker version 3.0.1
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>> Corosync version 3.1.9
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>> DRBD version 9.3.0
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>> So, the question is – what is the most correct way of implementing STONITH/fencing with fence_iomilan + diskless sbd (hpwdt, /dev/watchdog) ?
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> The correct way of using diskless sbd with a two-node cluster is not to use it ;-)
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> diskless sbd (watchdog-fencing) requires 'real' quorum and quorum provided by corosync in two-node mode would introduce split-brain which
> is the reason why sbd recognizes the two-node operation and replaces quorum from corosync by the information that the peer node is currently
> in the cluster. This is fine for working with poison-pill fencing - a single single shared disk then doesn't become a single-point-of-failure as long
> as the peer is there. But for watchdog-fencing that doesn't help because the peer going away would mean you have to commit suicide.
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> and alternative with a two-node cluster is to step away from the actual two-node design and go with qdevice for 'real' quorum.

Hmm ... the original description does mention qdevice, although it is
not quite clear where it is located (is there the third node?)

> You'll need some kind of 3rd node but it doesn't have to be a full cluster node.
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