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"? > + > +* We *advise against* using bond modes *balance-rr*, *balance-xor*, > + *balance-tlb*, or *balance-alb* for Corosync traffic. As explained above, > + they can cause asymmetric connectivity in certain failure scenarios. > + > +* *IEEE 802.3ad (LACP)*: This bond mode can cause asymmetric connectivity in > + certain failure scenarios as explained above, but it can recover from this > + state, as each side can stop using a bonded interface if it has not > received > + three LACPDUs in a row. However, with default settings, LACPDUs are only > sent > + every 30 seconds, yielding a failover time of 90 seconds. This is too long, > + as nodes with HA resources will fence themselves already after roughly one > + minute without a stable quorum. If LACP bonds are used for corosync > traffic, > + we recommend setting `bond-lacp-rate fast` *on the Proxmox VE node and the > + switch*! Setting this option on one side requests the other side to send an > + LACPDU every second. Setting this option on both sides can reduce the > + failover time in the scenario above to 3 seconds and thus prevent fencing. > + > +* Bond mode *active-backup* will not cause asymmetric connectivity in the > + failure scenario described above, but the affected node may lose connection > + to the cluster and, if HA is enabled, fence itself. > + > Separate Cluster Network > ~~~~~~~~~~~~~~~~~~~~~~~~ > _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
