A/B Port bit in Inquiry Data

Bob Snively Bob.Snively at Eng.Sun.COM
Tue Feb 3 07:24:37 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Bob Snively <Bob.Snively at Eng.Sun.COM>


I continue to state that you have complete information identifying the
path.  There is no other information you can obtain through the
standard SCSI command set.  Quality of service issues are addressed by
information exchanged with the fabric components, and since you can
precisely identify which port is where on the fabric, no additional
information is needed.

The tools are there, and I stand by my statement that there is no need
for a SCSI device to internally create an a/b concept or an active/alternate
concept when any QoS fabric can be attached to either port.


> >For that reason, it is certainly unclear to me that any additional
> >flag information is required to properly identify and manage multi-port
> >devices, including large RAID devices.  It is even less clear to me that
> >we want to drag in either an "a/b" concept or an "active/alternate" concept.
> >
> Hi Bob,
> In the future, some RAID device may have multiple paths to a LUN device
> thru a fabric. In this case, one path may be much faster than the other
> path and the system driver may want to take advantage of this extra
> bit of information that the LUN can provide about its paths.

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