SBP2 clarification

John Nels Fuller jfuller at microsoft.com
Mon Sep 15 16:12:41 PDT 1997


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* John Nels Fuller <jfuller at MICROSOFT.com>
*
NOTE: I've copied the T10 and Diskboys reflectors, as they are the
appropriate venue for SBP-2 questions.

If a LUN supports multiple initiators it will have a different fetch
agent CSR space for each as there will be a separate queue for each
initiator.  This is since an initiator is identified by its node ID and
a queue is constrained to be entirely within the initiator's node.
Therefore an additional initiator would have to have a separate node ID
and hence a separate queue and thus its own set of fetch agent CSRs.

Now that we've established the separate fetch agents for each initiator,
one must observe that there can be no guaranteed order of execution
between queues, at least from an initiator's perspective, because of the
asynchronous nature of an initiators appending to  queues and the fetch
agents reading from them.  So I think this is implementation dependant.
For example, one implementation may use a round-robin scheme and another
a priority scheme.

> ----------
> From: 	Srinivasa Addepalli
> Sent: 	Monday, September 15, 1997 10:38 AM
> To: 	p1394 at sun.com
> Subject: 	SBP2 clarification
> 
> I was going through SBP-2 document. I have following
> observations and questions.
> 
> If target supports mutilple units
>   Each unit will have its own Management CSR.
>   Each unit can have one or more logical units.
>   Each logical unit can support single initiator or multiple
>     initiators.
>   
> If the target allows multiple initiators ( for same LUN ),
>  will the target give
> different fetch agent CSR space for each initiator, Or does it
> give single fetch agent CSR space for all initiators in the logical
> unit? Or Is it implementation dependent?
> 
> It seems to me that having different fetch agent CSR space for
> each initiator is logical to me. Is it?
> 
> Is there are different fetch agents for same LUN ( if above 
> assumption is OK ), then they run independently. If so, in
> which order the command ORBs are executed? Does SBp-2 specify this
> or Is it completely implmentation dependent?
> 
> Thanks in advance
> Srini
> -- 
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