Command linking through switches

Bob Snively Bob.Snively at Eng.Sun.COM
Sun Mar 1 21:51:10 PST 1998

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


I am hoping that command linking through a switch will operate exactly
like command linking on a direct loop.  Each of the sequences in the
exchange is a separate Information Unit which is transmitted, received,
and managed in the proper sequence by the end-points (target and initiator)

If you need it, the architecture supports it.  However, the historical
usage that I am aware of (reducing selection overhead for firmware managed
selection) is not relevant any longer.  Most of the other potential
uses have also been over-taken by improved DMA and target architectures,
so the requirements for it are even weaker.

Be aware that in multi-initiator environments, ordering relative to
commands outside the linked set is not mandatory, so it cannot be depended on
as a replacement for proper driver design.  This is stated implicitly
and explicitly by various SAM chapters.

For all these reasons, I would be delighted to see it die from disuse.

Bob Snively			       Phone:	   (650) 786-6694
Sun Microsystems Computer Company      
Mail Stop UMPK 12-204
901 San Antonio Road		       E-mail:   bob.snively at
Palo Alto, CA 94303

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