Why are you installing from one USB stick to another?  The original image is bootable.  You can copy the initial image onto both.  I realize that's not the original task you were trying to do, but it would have less problems.

On Sun, Oct 16, 2011 at 6:51 PM, Juan Francisco Cantero Hurtado (via DragonFly issue tracker) <sinknull@leaf.dragonflybsd.org> wrote:

New submission from Juan Francisco Cantero Hurtado <iam@juanfra.info>:

Steps for reproduce:
- Download the last usb image from the mirrors.
- dd to your usb stick.
- Power off your computer.
- Conect two usb sticks to your computer. The first with the installer of
DragonFly. The seconds will be the destination of your installation.
- Boot the installer.
- Install DragonFly in your second usb stick. Use all the disk and hammer.
- Power off your computer.
- Disconnect the first usb stick.
- Power on your computer.
- Boot your usb stick.
- DragonFly doesn't find your root partition.

The old (usb) disk "da9x" is "da8x" now. Here exists two problems:
- In /etc/fstab the partitions point to "da9x".
- The same for /boot/loader.conf.

The installation in usb disks is useless. With this problem the user can't use
his or her usb disk in other computers with other order of usb disks. Also this
is very bad for IT departments.

I think the better solution is the support for UUID.

The same problem for other user:
- http://leaf.dragonflybsd.org/mailarchive/users/2011-09/msg00024.html

keyword: HAMMER, boot/loader, installer
messages: 10202
nosy: juanfra684
priority: bug
status: unread
title: DragonFly doesn't boot from usb stick

DragonFly issue tracker <bugs@lists.dragonflybsd.org>