Windows 2003+ MPIO with ALB and EVA Preferred Path?

[Sheldon Smith]

I am setting up several Windows 2003 servers with an EVA 4400. On the Windows hosts, I turn on ALB (Adaptive Load Balance) and leave MPIO load balancing set to SQST.
Question: Would I also set the Preferred Path (Failover/Failback) on the individual virtual disk to 'balance' the overall traffic between the two controllers? If not, what would prevent all virtual disks from getting controlled by the same controller, assuming the array is working normally?

[Víctor Cespón]

I you let MPIO regulate the access, in the vdisk properties you must set "No preference".

If one I/O comes to MPIO and the previous I/O has not yet been completed, MPIO will send it through another path (as it has queue lenght = 0).

[Sheldon Smith]

Thanks. Still, my second question: With the EVA Preferred Path set to None, what prevents all vdisks from getting picked up by one controller, leaving the other idle? That is, do the controllers load balance the vdisks between themselves? If so, anyone know how?

[IBaltay]

the only combination is set prefered path controller a/b failover/failback also for MPIO ALB, otherwise the controller will not return to its original (managing) role...

[Sheldon Smith]

Thank you.

Lastly: If Preferred Path is set to None on all vdisks, all hosts are using ALB and all paths are good, will the controllers ever spontaneously move a vdisk between themselves to reduce the load on a controller?

[IBaltay · Accepted solution]

ALB manages the host communication with the managing controller, it load balances its active paths... So if we want to have nicely balanced the controllers, we have to set preferred path with the failover/failback option on the EVA side, to return to the balanced controller situation also after one controllere failure/repair. In that case MPIO would switch to the second controller (failure of the first) but after the repair of the first it fails over role of the managing controller and ALB recognizes it and all will be balanced again
a) between the controllers (EVA set prefered path) and
b) between the paths of the managing controllers (MPIO ALB)

[Sheldon Smith]

Thanks to all!