2013-05-31 04:04 AM
I don't usually use the Systems Manager (I'm mostly a CLI-only guy), but I just tried it on our playground.
Results: The resync option does a normal resync _without_ changing the direction of the mirror. It does not matter whether you execute the resync on the source or the destination (as opposed to the CLI, where the node that you execute the resync on becomes the destination).
The reverse reysnc option re-establishes the mirror _with_ a change of direction, ie. the former source becomes the destination and vice versa. Again, it does not matter whether you do it on the source or destination.
The dialog box that appears and asks for confirmation should make it pretty clear what happens.
During the resync, a new relationship will be created (with the direction reversed). The original relationship will remain in the broken-off state, and can probably be removed in most circumstances (depends on why you're reversing in the first place).
Tested with Systems Manager 2.2rc1.