how to make fixed Direct Access device (da) ID

[Jin Guojun [VFFS]]

It is awkward that dynamically and/or statically attaching SCSI hard 
drive and
USB hard drive to the system will have different da IDs.
For example, boot system with a SCSI drive (SCSI = 1), will have a da0 
for this
SCSI drive. Then plugging in a USB hard drive, which will be configured 
as da1.

If boot system with both drives online, system will boot from SCSI drive 
fine till
mounting root point. It fails because USB drive has da0 and SCSI drive 
has da1.

Is there anyway to configure the system to have fixed da ID for SCSI 
drive or
even for USB drive regardless if they are dynamically/statically 
attached to the
system?

    -Jin