66  IBM System Storage N series Hardware Guide
Enable ACP on the storage system by entering the following command at the console:
options acp.enabled on
Verify that the ACP cabling is correct by entering the following command:
storage show acp
For more information about cabling SAS stacks and ACP to an HA pair, see IBM System 
Storage EXN3000 Storage Expansion Unit Hardware and Service Guide, which is available at 
this website:
http://www.ibm.com/storage/support/nas
6.2  EXN4000 disk shelves cabling
This section describes the requirements for connecting an expansion unit to N series storage 
systems and other expansion units. For more information about installing and connecting 
expansion units in a rack, or connecting an expansion unit to your storage system, see the 
Installation and Setup Instructions for your storage system.