8.0 installer failure

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I just tried to install 8.0 (for work, to be sure).  I sucked over the
flash-drive installer
(http://cdn.netbsd.org/pub/NetBSD/NetBSD-8.0/images/NetBSD-8.0-amd64-install.img.gz),
gunzipped it, and wrote it to a thumb drive.

It booted, though I had to use an external USB hub; without it, for
reasons I don't have even guesses at, the installer kernel did not find
the thumb drive and prompted for root (with, of course, no way for me
to specify the correct value, both because sd0 wasn't found and because
as far as I can tell keystrokes were being ignored).

But, when I tried to install, it failed.  Everything went fine until it
tried to installboot.  Here's a ten-finger copy of what I see then:

     Status: Command failed
    Command: /usr/sbin/installboot -o console=pc,speed=9600 /dev/rwd0a /usr/mdec
/bootxx_ffsv2
     Hit enter to continue
--------------------------------------------------------------------------------
installboot: Old BPB too big, use -f (may invalidate filesystem)
installboot: Set bootstrap operation failed

(The "Command failed" and the command are blue-on-white; the rest is
white-on-blue.)

There is another problem: it appears to have created an FFSv2
filesystem (according to both the above and the newfs options shown
when it was making the filesystem), even though in the partitioning
setup it shows that partition as being FFSv1.  This leaves me with no
obvious way to try my first guess at fixing it - falling back to FFSv1
(which I would prefer anyway).

There was stuff on the disk before; I'll try wiping the first megabyte
or so to zeros to see if that helps.  If not, I may experiment with
other things, but this is an aspect of peecees I don't really
understand, so I don't expect to get too far.

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