SCF Reference Manual for the Storage Subsystem (G06.28+, H06.05+, J06.03+)

Considerations for SWITCH DISK
If you attempt to switch the primary and backup paths but the backup path is unavailable, the
paths are not switched.
If the specified path is already active, the SWITCH command has no effect.
Use the STATUS DISK command to verify the path switch.
Switching the path to the backup controller can create a SAC ownership conflict in G06.10
and earlier RVUs. See “Understanding SAC Ownership” (page 123).
Changing the Active Path for a Disk 113