SD(4) BSD Programmer's Manual SD(4)NAMEtg - machine-independent SCSI target driver
SYNOPSIS
tg0 at scsi? target 0
tg* at scsi? target ?
DESCRIPTION
The tg driver exists primarily to provide an attachment point for logical
units on the Small Computer System Interface (ANSI X3.131-1992) bus. On
finding a target, the system probes for all eight possible logical units;
those that respond are treated as directed by the rest of the system con-
figuration. Note that these logical units (or ``LUNs'') differ from the
system's idea of a ``unit''. For instance, one drive might be ``at tg0
unit 0'' and another might be ``at tg1 unit 0''; these must be different
system units even though they have the same SCSI LUN.
The clone entry tg* should be listed last; this will automatically match
any otherwise unmatched targets. Additional instances of tg devices can
be ``wired'' to particular controllers and/or target numbers, and logical
units can then be wired to these target devices, with the rest defaulted
from clones. The cloned entries will be taken in the order they are
found, while the ``wired'' configuration entries will reserve those par-
ticular slots, even if the drives are temporarily out of service.
BUGS
The system needs a way to open a target even if it has no configured
LUNs, or at least a way to open each SCSI controller, and/or to ask for
another configuration scan.
BSDI BSD/OS March 23, 1993 1
