Should automatic path group failback be disabled on all cluster configurations? This is certainly what I have assumed in order to avoid cases where the nodes of a cluster are battling one another trying to activate different path groups for the same block device. Yet, this approach has the disadvantage of potentially resulting in an unbalanced assignment of block devices to path groups over time, that is, too many block devices could be active on the same path group. Most asymmetric storage systems are not meant to reserve a path group as a hot standby for all logical units, but instead statically balance the assignment of logical units to path groups in order to balance the overall IO load. Another approach is to only initiate automatic failback from a host if the initial failover was initiated by that host. Otherwise, assuming the currently active path group contains active paths, simply accept the externally initiated path group re-assignment away from the highest priority path group and start using paths from the active path group. This approach certainly requires the tracking of path group assignment/activations away from the highest priority path group initiated by a host on a block device basis. Seems like the multipath target driver in the kernel is the best place for this. Multipathd could pull out this information and use it to further conditionalize the autoamtic path group failback.
