If you have only one vio server hosting client partitions, you need to shutdown the client partitions first. Then shutdown, perform maintenance on VIO, etc., restart VIOS in operational status, and then start the client partitions.
The way to prevent extended downtimes for client partitions is to implement a dual-vios solution such that one VIOS is the backup of the other. There is a course on that (IBM course code AU78, come join my class in Holland on the 22nd
), and I thought a FAQ or an article on setting up SAN disks and a dual VIO in the rootvg articles. I know I started it
