[CentOS] Booting from an external USB drive?

Thu Dec 1 16:33:18 UTC 2005
Bart Schaefer <barton.schaefer at gmail.com>

Is it possible?

Booting the installer from the CD works, finds the USB drive, and
allows me to put the root filesystem on it.  I put the /boot partition
on the internal hard drive and installed GRUB in the boot record of
that partition.

GRUB shows the menu and begins booting, but eventually fails with the
error that /dev/sda5 (the external partition) does not exist.

I was hoping (perhaps in vain) that initrd would provide the necessary
modules/hooks to mount the USB device.  Is there some step of the
installation that I'm missing, or something extra that I need to do by
hand, like in the old days when LILO had to be explicitly told about
SCSI cards?