freebsd stable - Aug 2009 - 8.0-BETA3 cannot mount root while booting from USB HDD: no da0

Hi!

I'm trying to boot FreeBSD 8.0-BETA3 from USB HDD,
GENERIC kernel. It loads and initializes just fine,
detects all devices just right, including umass0 for USB HDD.
However, it does not create da0 and cannot mount root filesystem,
bailing out to "mountroot>" prompt.

It does not list da0 if I type "?", only ad0 for internal ATA device
(ad0 is CompactFlash, not bootable yet).

I've tried to increase kern.cam.scsi_delay to 60000,
it changes nothing, only increases delay.

I have build-box and can apply patches, if any.
Please help.

Eugene Grosbein