SCAM and boot devices

HCurley at HCurley at
Sun Feb 11 15:55:41 PST 1996

* From the SCSI Reflector, posted by:
* HCurley at
Friends in SCSI,

Many host adapters require that the boot device be SCSI ID 0 or SCSI ID 6.
 With some host adapters, the ID is configurable by modifying the host
adapter BIOS.  In any regard, system expects to see a boot device at a
particular location.

When we build a new SCSI bus with SCSI compliant devices, probably a disk
drive will end up with ID 0, or ID 6 as required for boot.  We will then
build the system on that device.  Then, when we add a new device and the
addresses are reassigned, that device is no longer at the proper location for
booting!  You and I can figure out how to fix the problem by changing the
devices current addresses, or boot from a different SCSI ID, but the whole
purpose of SCAM is to allow non-computer literate people plug new devices
onto their SCSI bus and have them work without understanding all about
configuration and termination.

I can also see a problem with the following new configuration:  Brand "Z" dot
matrix printer with current address 3, Brand "Y" printer laserjet printer
with current address 3, Brand "X" scanner with current address 3, Brand "W"
tape drive with current address 3, Brand "V" disk with current address 0 and
a host adapter that requires the boot device on SCSI ID 0.  The dot matrix
printer gets ID 3, the laserjet gets 2, the scanner gets 1, the tape drive
gets 0, and the disk gets 6 (assuming the host adapter is 7).  Now, you will
try to boot from the tape.

How does SCAM avoid the problems of the intended boot device being assigned
to the wrong address, either on initial configuration or later when adding a
new device?

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