No-one is perfect. I recently added some shelves to the wrong location of a stack, breaking the design rule of a single speed transition between 3G and 6G shelves, and didn’t find out until after the new disks were added to an existing aggregate. Under normal circumstances, you can officially hot remove disk shelves from a system running ONTAP 8.2.1 or later. Assuming they don’t have data on them, which these ones did.

Fortunately ONTAP doesn’t require symmetric SAS topologies, so I did the following to resolve it:

1. Aim to recable the IOM B stack
2. Failover and take node 2 out of service
3. Disconnect SAS cable from node 1 (yes, node 1) to IOM B
4. Recable IOM B’s SAS stack
5. Disconnect node 2’s connection to the IOM A stack
6. Bring up node 2, failback
7. At this point, node 1 and node 2 have different, non redundant topologies
8. Failover node 1 to node 2
9. Recable IOM A stack
10. Reconnect redundant connections for IOM A and IOM B to bring node 2 back into MPHA
11. Failback to node 1

Tada, all done, non-disruptive (system is iSCSI only – CIFS without SMB3 Continuous Availablity would result in session disconnects)