gmirror ate my disk

[Steve Franks]

So, I've got 2 gmirrors working fine for 6 months or so.  Didn't have
any issues.  One got full, however, so I decided to buy fresh disks
and make a new one.

Did exactly what I did the first time: fdisk/label/copy data to one
disk, add it to the mirror.  added another disk, got to DEGRADED 100%.
Gmirror seems to hang there forever unless you reboot -

Now, system won't boot (aka /bin/sh or pathname) -> why? -> mount
gives "incorrect superblock" for /dev/mirror/gm1.  Took gm1 out of
fstab, or course, then ran fsck, which echoed the concerns about
incorrect super block.  Rebooted, now fsck just says, "Could not
determine filesystem type".  What's my best way to proceed?  It took
all &*%#@ day to mirror up those 2 disks, and I'd rather not repeat
the process if there is something I can do to recover the data as is -
only if I can trust the mirror after recovery, of course.

Thanks,
Steve