Applied Bill's patch to use the "raw" version of a disk if it's there.

user_tools/linux/recovery.sh

 #!/bin/sh
 #
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # This attempts to guide linux users through the process of putting a recovery
 # image onto a removeable USB drive.
 #
 # We may not need root privileges if we have the right permissions.
@@ skipping 804 matching lines @@
 "
 
 # Unmount anything on that device.
 echo "unmounting..."
 for tmp in $(mount | grep ^"/dev/${user_choice}" | cut -d' ' -f1); do
   unmount_partition "$tmp"
 done
 
 # Write it.
 echo "copying... (this may take several minutes)"
+
+# Many BSD variants provide both normal /dev/FOO and raw /dev/rFOO devices,
+# with the raw path being much faster. If that device exists, we'll use it.
+if [ -e /dev/r${user_choice} ]; then
+  user_choice="r${user_choice}"
+fi
 dd bs=4194304 of=/dev/${user_choice} if="$image_file" conv=sync ||
   ufatal "Unable to write the image."
 sync
 
 echo "
 
 Done. Remove the USB drive and insert it in your Chrome notebook.
 
 "
 
 prompt "Shall I remove the temporary files now? [y/n] "
 read tmp
 case $tmp in
   [Yy]*)
     cd
     \rm -rf ${WORKDIR}
     ;;
 esac
 
 exit 0