Subject: [storm] iSCSI UML Model re-visit

From: "Mallikarjun Chadalapaka" <[email-masked]>
Date: Thu, 25 Jun 2009 18:11:32 -0700

All,

After the last UML model proposal I posted on this mailing list, I had a
couple of offline conversations.  During these, I stumbled into SCSI
Extended Copy (or what appear to be the implied semantics of it) and it
seems that neither RFC 3720 nor my earlier proposed UML model sanction legal
iSCSI implementations of Extended Copy.

Here are the SCSI Extended Copy implied semantics as I understand:

- "Copy manager", the entity that receives the SCSI Extended Copy command
and orchestrates copy operation to conclusion, actually consists of a device
server part (which receives the command) and an application client part
(which copies data from "copy source" to "copy destination")

- Device server part of the copy manager runs logically in a SCSI Target
Device (actually in a Logical Unit in a target), let's call it Target-1.
Application client part of the copy manager runs logically in a SCSI
Initiator Device, let's call this Init-1

- Both Init-1 and Target-1 must be contained in an umbrella SCSI Device with
a shared SCSI Device Name

- All this implies that in order to correctly support SCSI Extended Copy,
iSCSI has to support an "umbrella node" concept that can contain an iSCSI
Initiator Node and an iSCSI Target Node 

RFC 3720 does not sanction such an umbrella node - an iSCSI Node is either
an Initiator Node or an Target Node.  So this will need to be tackled in the
new draft.  

I created a new "Approach B" model mapping to address this issue.  The new
UML model is now available online at:

http://chadalapaka.com/Documents/Approach%20B-%20iSCSI%20and%20SAM-4%20Class
%20Modeling.pdf 

Comments are welcome.  Thanks.

Mallikarjun