gmirror + subset of partitions gjournal'd, autosync setting?

[Carl]

I've built a GEOM mirror on a single slice of a single disk and am about 
to insert the second disk. Of the partitions in the mirror, I made only 
a few of them gjournal'd. I've seen it recommended that one disable 
autosynchronization for the mirror if using journaled filesystems.

1. Is that recommendation a must or a nice-to-have? What are the actual 
consequences of not taking that advice?

2. In a case like mine, the non-journaled partitions need 
autosychronization enabled to benefit from being mirrored, right?

3. Exactly how would I disable autosynchronization for the journaled 
partitions in the mirror, but not for the rest?

Carl                                             / K0802647