RE: Command Queue Depth (was asymmetric/Symmetric)

[Peter Johansson <PJohansson@ACM.org>]

At 08:06 PM 9/6/00, Jim McGrath wrote:

>The issue of buffer space allocation for multiple initiators has a long 
>and troubled history in SCSI.  We have never been able to come up with a 
>good answer.
>
>Note: the same problem has plagued other attempts to allocate device 
>resources between multiple initiators, like command queue space.  In 
>general policies with respect to multiple initiators are not really 
>standard in the SCSI world.

Jim's response is correct as far as it goes, but it ignores the solution 
adopted in SBP-2, which neatly finesses these issues by leaving the 
resources in the initiator.

In fairness, it's likely that the appropriateness (or lack thereof) of an 
iSCSI solution similar to SBP-2 has been ignored in these discussions 
because SBP-2 has been less widely implemented than parallel SCSI or FCP.

Is it possible that the SBP-2 approach is relevant to iSCSI? That is, put 
the initiator in the role of "memory server" and let the target manage when 
and how its own resources are used to effect the transfer of data. This 
might make sense if the model places more of the assumed resources 
(principally memory) in the initiator.

Can this be effected efficiently?




Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
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