granularity of load balance

Question

what's the granularity of load balancing? I/O or LUN. in a extreme case, if i have only one LUN, will all I/O to this lun use different path?

Conor · Accepted Answer

The sequence number of each fibre channel IO (frame) is contained within the frame itself, all part of the Fiber-Channel protocol.

Conor · Answer

PowerPath load-balancing is per IO.PowerPath load balancing in active/active environment works as follows [very rough explanation]: PowerPath will use the path previously chosen for the I/O against the same device as long as the load on this path is not too high. This explains why, as long as the load generated by the host is not too high, the I/Os are always sent along the same path (giving the impression that PowerPath load-balancing is broken!). [can be seen from powermt display - you will see Q-IO's more on one path than others]In summary, unless the path that was last used for I/O to that device is very busy, PowerPath will route the I/O along the same path. Otherwise, it will route the I/O down an alternate path (balance the I/Os down alternate path). Alternately you can chose the round-robin policy where each IO is set down a different path in turn.

SKT2 · Answer

Also when ISL connected nodes are in the situation and w/o a trunking license ( NOT load balanced rather just fail over) then also you may observe the Q-IO are different/higer on some paths

dingding1 · Answer

if there are 100 I/O to one LUN, say IO1 to IO 100 order by time, and these I/O is distributed in many path, which part will keep the order? and how to keep the order.

dingding1 · Answer

if there are 100 I/O to one LUN, say IO1 to IO 100 order by time, and these I/O is distributed in many path, which part will keep the order? and how to keep the order.