There’s a nice article about “round-robin” load balancing on SystemsArchitech which got me a bit dazzled about this new functionality:
esxcfg-mpath – lun <*.lun> —policy custom –H minq –T any –C 0 –B 2048
The policy states that the LUN should utilize a custom policy that determines which (of two) HBA to utilize based on the minimum queue length. This HBA selection is triggered every 2048 blocks transmitted to a given LUN over the same target. The policy will use any targets available to either of the two HBAs. In using storage that manages host port load-balancing, LUNs will only have two paths (one per fabric) and the storage array will perform storage array host port balancing from within its own management. With other storage arrays it is typical to perform this host port balancing from the hosts accessing the given storage array.
With 10 ESX hosts set with this policy wouldn’t it probably cause path thrashing on an active/active SAN? You never know which controller will access a specific LUN and if your unlucky it will be switching from controller A to controller B every millisecond. Anyone else any thoughts on this new feature and the possible danger?