RE: iSCSI: new state diagrams for rev09

[Black_David@emc.com]

A bit tardy, but I'd like to thank everyone whose efforts
have contributed to these diagrams and explanations.  Getting
error behavior completely specified is not easy, and very
important to the overall specification of iSCSI.  Keep up
the good work.

Many Thanks,
--David 

> -----Original Message-----
> From: Mallikarjun C. [mailto:cbm@rose.hp.com]
> Sent: Friday, November 02, 2001 1:33 PM
> To: ips
> Subject: iSCSI: new state diagrams for rev09
> 
> 
> All:
> 
> Consequent to the feedback I received both online and
> offline, iSCSI state diagrams are considerably revamped.
> Thanks to all those who provided the feedback.  The new
> state diagrams are posted at:
> 
> 	http://storage-arch.hp.com/iscsi_states_rev09.pdf
> 
> The ASCII forms of the above are currently part of rev 08-90
> draft that Julian posted on his web.
> 
> The major changes are -
> 
> - The initiator and target state machines are split for 
>   both standard connection diagram and session state 
>   diagram.  It is hoped that this separation makes it
>   easier to follow.
> 
> - Several (informative, but) non-essential states were
>   eliminated, since they were waiting for internal events 
>   (like acquiring resources) that are likely non-existent 
>   in good implementations.  That leaves us with a 7-state
>   machine for both initiator and target.
> 
> - The reduction of states has a salutary effect on the ASCII
>   representation.  I was able to translate all the diagrams
>   into ASCII!
> 
> - The state descriptions are more descriptive now, specifically
>   calling out the event(s) that the state machine is waiting 
>   for in that state.
> 
> - The transition descriptions are also more descriptive,
>   listing the set of events that causes the given transition
>   for each of the roles.
> 
> - The "connection recovery state diagram" has been renamed 
>   as "connection cleanup state diagram" since the word "recovery"
>   was inadvertently overloaded.  Connection recovery (the 
>   act of reassigning the task allegiance to a different connection)
>   happens outside the scope of this state machine depending on
>   the operational ErrorRecoveryLevel - all this diagram
>   specifies is the dynamics of gracefully closing an active 
>   iSCSI connection, perhaps replacing with a new connection.
> 
> - Consequent to the above and for general clarity, some 
>   states have been renamed to reflect the "wait reason" better.
> 
> - Certain missing/incorrect transitions are now fixed -
>   like the "close the session" Logout handling etc.
> 
> - I added some text on the first slide that describes the
>   design philosophy behind the current model, perhaps also 
>   can be called design assumptions.
> 
> 
> I have only one (likely) open issue on my list.  I received
> feedback from one reviewer that the _description_ of the diagrams 
> is not "traditional" - for example, the current tabular format 
> captures the transitions (each caused by a set of events) in 
> a state-state matrix, but does not describe them in terms of 
> an event-state matrix for each state (which would run into 
> several pages).  The current description scheme seemed quite 
> acceptable to myself (and also to Julian among others) - but 
> I am open on this.  Please comment if you strongly feel about 
> this issue.
> 
> Thanks! 
> -- 
> Mallikarjun 
> 
> 
> Mallikarjun Chadalapaka
> Networked Storage Architecture
> Network Storage Solutions Organization
> MS 5668	Hewlett-Packard, Roseville.
> cbm@rose.hp.com
>