Recently upgraded my FreeBSD install to FreeBSD 9.1-stable from the 9-stable branch. I have two SATA hard drives (/dev/ada0, /dev/ada1) in a geom mirror, with nothing between :
[/dev/ada0, /dev/ada1] --> /dev/mirror/gm0, which I then partition for root etc.
After upgrading from 9.0-stable to 9.1-stable, I found these messages on the console:
GEOM_MIRROR: cancelling unmapped because of ada0 GEOM_MIRROR: cancelling unmapped because of ada1 GEOM_MIRROR: Device mirror/gm0 launched (2/2).
Everything still seems to work, the mirror seems healthy and the machine works just fine, peformance is fine.