Use disk resize only when mirroring is permanently disabled.
If you try to run disk resize on a device that is mirrored, you see:
disk resize can proceed only when mirroring is permanently disabled. Unmirror secondary with mode = 'remove' and re-execute disk resize command.
The primary device is active while the secondary device is temporarily disabled and produces the same error as shown above.
The secondary device is active while the primary device is temporarily disabled and produces an error with this message:
disk resize can proceed only when mirroring is permanently disabled. Unmirror primary with mode = 'remove' and re-execute the command.