SAM definition of SCSI Device

Neil T. Wanamaker ntw at
Wed May 26 11:24:39 PDT 1999

* From the T10 Reflector (t10 at, posted by:
* "Neil T. Wanamaker" <ntw at>
At 07:57 AM 5/26/99 -0700, Bob Snively wrote:
>Selecting one portion of Ralph's discussion:
>> My understanding is that the purpose behind this move to define an
>> SCSI Device as having only one port relates to the issues you raise.
>> The move intends to state clearly that the SCSI physical and transport 
>> layers do not provide any support whatsoever for multi-path implementa-
>> tions.  This certainly is true for the parallel SCSI bus.  But, the 
>> technical editor for FCP-2 is adamant that it's an architectural 
>> 'feature'; I assume because he believes that it would be wrong to add 
>> multi-path address resolution features to FCP-2.
>Actually, for those who are truly dedicated to "dynamic multi-pathing"
>a la ESCON, Fibre Channel provides the feature through its hunt group
>definitions with no change to SCSI or to FCP-2. 
To emulate the capabilities we are talking about here, both the initiator
and target must belong to (model 3 or 4) hunt groups. Since no switch I can
purchase supports hunt groups, this may not be meaningful...

Further, hunt group models 3/4 require that the exchange (and for 4,
sequence) management is embedded in a common shared entity. This would
appear to require an HBA and a controller (rather than switch) to manage
the hunt groups. This perhaps would not require SCSI or FCP-2 changes, but
would require architectural changes to the controllers and hosts.
| Neil T. Wanamaker         Crossroads Systems, Inc.              |
| ntw at        			  		                      	 |    
| (512)794-2727                                                   |
| (512)349-0304 FAX    Web URL -        |
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