Ah ha!

I originally created one drive, then used dd to copy the first sectors
from one drive to the other.  Clearly this was a mistake...

writing a new disklabel to wd1 fixed it.  Magic!  :)

--Michael

Thor Lancelot Simon wrote:
> On Wed, Dec 05, 2007 at 12:10:34AM -0000, explorer@flame.org wrote:
>> 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)
> 
> Two BIOS drives have the same signature because they have exactly the same
> contents in their first sectors.  The kernel can't be certain which one you
> actually booted from, so you might get / mounted from the other one by
> accident.  Typically happens when one clones disks with dd instead of using
> the tools to partition them -- the tools write a unique signature into
> place...
>