On Wed, Jul 21, 2021 at 11:50 AM Frank D. Engel, Jr. <fde...@fjrhome.net> wrote: > > OpenVMS can do this sort of thing without a requirement for fencing (you > still need a third disk as a quorum device in a 2-node cluster), but > Linux (at least in its current form) cannot. From what I can tell the > fencing requirements in the Linux solution are mainly due to limitations > of how deeply the clustering solution is integrated into the kernel. >
This is a common misunderstanding. *All* cluster solutions use fencing. Maybe they do not call it "fencing" and many cluster solutions use self-fencing (suicide), but it does not change the basic fact - cluster needs fencing. Pacemaker supports self-fencing. It does not support arbitration using SCSI reservations that you mean here. It is not related to "kernel integration" at all - you can do arbitration completely in user space. It is just that someone needs to implement it. Given that in the case of shared storage there is already a solution - SBD - and SCSI arbitration cannot be used without shared storage it is not clear what will be gained by implementing it. Better would be to spend the efforts improving pacemaker/sbd integration. Arbitration fits more in corosync than stonith. Arbitration does not kill other node - it decides which node remains in quorum and node that lost commits suicide. > There is an overview here: > https://sciinc.com/remotedba/techinfo/tech_presentations/Boot%20Camp%202013/Bootcamp_2013_Comparison%20of%20Red%20Hat%20Clusters%20with%20OpenVMS%20Clusters.pdf > > > I am wondering how much of what OpenVMS does could be integrated into > Linux in the future to simplify the HA clustering situation. This is one > thing OpenVMS currently does FAR better than any other platform I've > come across, so it is likely there is still much to be learned from it. > > > On 7/20/21 6:45 PM, Digimer wrote: > > On 2021-07-20 6:04 p.m., john tillman wrote: > >> Greetings, > >> > >> Is it possible to configure a two node cluster (pacemaker 2.0) without > >> fencing and avoid split brain? > > No. > > > >> I was hoping there was a way to use a 3rd node's ip address, like from a > >> network switch, as a tie breaker to provide quorum. A simple successful > >> ping would do it. > > Quorum is a different concept and doesn't remove the need for fencing. > > > >> I realize that this 'ping' approach is not the bullet proof solution that > >> fencing would provide. However, it may be an improvement over two nodes > >> alone. > > It would be, at best, a false sense of security. > > > >> Is there a configuration like that already? Any other ideas? > >> > >> Pointers to useful documents/discussions on avoiding split brain with two > >> node clusters would be welcome. > > https://www.alteeve.com/w/The_2-Node_Myth > > > > (note: currently throwing a cert error related to the let's encrypt > > issue, should be cleared up soon). > > > > _______________________________________________ > Manage your subscription: > https://lists.clusterlabs.org/mailman/listinfo/users > > ClusterLabs home: https://www.clusterlabs.org/ _______________________________________________ Manage your subscription: https://lists.clusterlabs.org/mailman/listinfo/users ClusterLabs home: https://www.clusterlabs.org/
