This message just means the system found two bootable drives when it
was searching for root devices.  Or, rather, it found two drives with
potential root partitions.  I've seen it on machines I've booted where I
have a broken raid1 mirror, and I'm using the second broken piece as a
root drive while I fix things up.
-Brian

On Dec 5, 12:10am, explorer@flame.org wrote:
} Subject: Odd dmesg log messages
} 
} The raid0 messages are pretty obvious.  I have raid0 auto-conf'd
} via raidctl, and I have raid0.conf in /etc.  The WARNING one confuses me...
} 
} raid0: RAID Level 1
} raid0: Components: /dev/wd0g /dev/wd1g
} raid0: Total Sectors: 566273088 (276500 MB)
} WARNING: double match for boot device (wd0, wd1)
} boot device: wd0
} root on wd0a dumps on wd0b
} root file system type: ffs
} raid0: Device already configured!
} 
} I suspect I can find the source (I can commit after all, if I can't grep
} I'd really be lame) but when I find it, I will be tempted to make it clear
} about what was searching for the boot device, and why it thinks either can be
} it.
} 
} --Michael
>-- End of excerpt from explorer@flame.org