SAN Pathing on an Active/Passive Array Part II

In a previous post I spoke of the issues around SAN Pathing on an Active/Passive Array. Today I met with VMWare EMC and our internal storage team to discuss this. I was slightly incorrect on how ESX decides where to assign a path. ESX issues a SCSI inq command and the first path to respond is used. So, because the first card to come up issues the command first, it usually takes the path. But depending on load of the array and fabric, the other card could be used. In talking through the issue though with everyone we came to a couple conclusions.

1. This can be done.
1. Build a table of the wwn from both SP.
2. Determine what SP a LUN is on from the wwn of the SP.
3. Determine what path on the second HBA is on the same SP.
4. Check if active path is already on preferred HBA (every other LUN alternates HBA)
5. If not on preferred HBA disable all but active path and path preferred to move to, the path being the ON but not ON ACTIVE path is not enough.
6. Disable ON ACTIVE path to move to other HBA.
7. Re-enable all paths.
8. Continue though all LUNS
2. In most environments the effort is not worth the benefit though.

So, we are going to keep an eye on HBA utilization and see if a bottleneck appears. At that point we may pursue the script above.