This is a discussion of the SP system implementation of root volume group mirroring and of using alternate root volume groups. It gives a brief description of common terminology and mirroring support in AIX. It does not provide a complete description of AIX mirroring or volume group support. For that information, reference the appropriate AIX publications.
You can mirror root volume groups so that you have a backup or two of the same version of AIX always ready and waiting to take over in the event of a disk failure. You can also set up alternate root volume groups. That means you can configure a different root volume group, one that contains another version of AIX on another disk or set of disks. Then on different occasions you can boot a node from one root volume group or another. For instance you might want two sets of disks so that you can switch from operating with one level of AIX to operating with another, perhaps to test a new installation before you use it for production work.