You can use disk resize command only when mirroring is permanently disabled. If you try to run disk resize on a device that is mirrored, you see this:
disk resize can proceed only when mirroring is permanently disabled. Unmirror secondary with mode = 'remove' and re-execute disk resize command.
When mirroring is only temporarily disabled, two scenarios can arise:
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.
Increasing the size of a mirrored device
Permanently disable mirroring on the device.
Increase the size of the primary device.
Physically remove the mirror device (in case of file).
Reestablish mirroring.
