Use this tab to control the submirrors that make up this mirror. You can:
Attach Submirror to the mirror to provide additional redundancy.
Remove Submirror if the submirror is no longer needed.
Online Submirror to restore a submirror to active duty.
Offline Submirror to temporarily disable writes to and reads from a submirror (perhaps to run a backup against the submirror while the mirror continues to function).