On 04/21/2017 10:10 AM, Kristoffer Grönlund wrote: > Ken Gaillot <kgail...@redhat.com> writes: > >>>> I think it works differently: One task periodically reads ist mailbox slot >>>> for commands, and once a comment was read, it's executed immediately. Only >>> if >>>> the read task does hang for a long time, the watchdog itself triggers a >>> reset >>>> (as SBD seems dead). So the delay is actually made from the sum of "write >>>> delay", "read delay", "command excution". >> I think you're right when sbd uses shared-storage, but there is a >> watchdog-only configuration that I believe digimer was referring to. >> >> With watchdog-only, the cluster will wait for the value of the >> stonith-watchdog-timeout property before considering the fencing successful. > I think there are some important distictions to make, to clarify what > SBD is and how it works: > > * The original SBD model uses shared storage as its fencing mechanism > (thus the name Shared-storage based death) - when talking about > watchdog-only SBD, a new mode only introduced in a fork of the SBD > project, it would probably help avoid confusion to be explicit about > that. > > * Watchdog-only SBD relies on quorum to avoid split-brain or fence > loops, and thus requires at least three nodes or an additional qdevice > node. This is my understanding, correct me if I am wrong. Also, this > disqualifies watchdog-sbd from any of Digimers setups since they are > 2-node only, so that's probably something to be aware of in this > discussion. ;)
There is no way around the '2 physical devices are not enough for an HA-cluster' paradigm ;-) And Watchdog-only SBD isn't one either although it helps you to make three nodes without any additional physical device (stonith-device, disk, ...) work as a reliable cluster. > > * The watchdog fencing in SBD is not the primary fence mechanism when > shared storage is available. In fact, it is an optional although > strongly recommended component. [1] As strongly recommended as fencing in general I would say ;-) Regards, Klaus > [1]: We (as in SUSE) require use of a watchdog for supported > configurations, but technically it is optional. > -- Klaus Wenninger Senior Software Engineer, EMEA ENG Openstack Infrastructure Red Hat kwenn...@redhat.com _______________________________________________ Users mailing list: Users@clusterlabs.org http://lists.clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org