On 25/07/2025 14:23, Mira Limbeck wrote: > > > On 7/25/25 13:50, Friedrich Weber wrote: >> On 25/07/2025 13:39, Friedrich Weber wrote: >>> [...] >>> +Corosync Over Bonds >>> +~~~~~~~~~~~~~~~~~~~ >>> + >>> +Using a xref:sysadmin_network_bond[bond] as the only Corosync link can be >>> +problematic in certain failure scenarios. If one of the bonded interfaces >>> fails >>> +and stops transmitting packets, but its link state stays up, some bond >>> modes >>> +may cause a state of asymmetric connectivity where cluster nodes can only >>> +communicate with different subsets of other nodes. In case of asymmetric >>> +connectivity, Corosync may not be able to form a stable quorum in the >>> cluster. >>> +If this state persists and HA is enabled, nodes may fence themselves, even >>> if >>> +their respective bond is still fully functioning. In the worst case, the >>> whole >>> +cluster may fence itself. >>> + >>> +For this reason, our recommendations are as follows. >>> + >>> +* We recommend a dedicated physical NIC for the primary Corosync link. >>> Bonds >>> + can be used as additional links for increased redundancy. >> >> These recommendations are still not 100% clear: Are we fine with a setup >> with >> >> - link 0: dedicated corosync link >> - link 1: corosync link over a bond with a problematic mode (such as >> balance-rr or LACP with bond-lacp-rate slow) >> >> ? >> In my tests, as long as the dedicated link 0 is completely online, it >> doesn't matter if a bond runs into the failure scenario above (one of >> the bonded NICs stops transmitting packets), corosync will just continue >> using link 0. But as soon as link 0 goes down and the failure scenario >> happens, the whole-cluster fence may happen. So should our >> recommendation be the relatively strict "if you put corosync on a bond >> (even if it is only a redundant link), use only active-backup or >> LACP+bond-lacp-rate fast"? > > I'd say yes, the recommendation should be either dedicated link > directly, or a bond as redundant link with active-backup or > LACP+lacp-rate fast only.
Thanks for the input. I've rephrased the section (and did some other adjustments) to make it clear that the caveats apply whenever a bond is used for corosync traffic. v3: https://lore.proxmox.com/pve-devel/20250725140312.250936-1-f.we...@proxmox.com/T/ _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
