RE: iSCSI question

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Pat,

Seems alright.

-Shahram

> -----Original Message-----
> From: pat_thaler@agilent.com [mailto:pat_thaler@agilent.com]
> Sent: Friday, August 09, 2002 1:10 PM
> To: Shahram Davari; pat_thaler@agilent.com; pkoning@equallogic.com
> Cc: ips@ece.cmu.edu
> Subject: RE: iSCSI question
> 
> 
> Shaharam,
> 
> I agree that the table by itself is not clear, but that the 
> text of the section clearly states things. That is why I 
> suggested a change to that table:
> 
>   +-------------------+--------------------------------------------+
>   |ErrorRecoveryLevel |  Associated Error recovery capabilities    |
>   +-------------------+--------------------------------------------+
>   |        0          |  Session recovery class                    |
>   |                   |  (Section 5.14.4 Session Recovery)         |
>   +-------------------+--------------------------------------------+
>   |        1          |  Digest failure recovery (See Note below.) |
>   |                   |  plus all ErrorRecoverLevel 0 capabilities |  
>   +-------------------+--------------------------------------------+
>   |        2          |  Connection recovery class                 |
>   |                   |  (Section 5.14.3 Connection Recovery)      | 
>   |                   |  plus all ErrorRecoverLevel 1 capabilities |
>   +-------------------+--------------------------------------------+
> 
> Pat
> 
> 
> -----Original Message-----
> From: Shahram Davari [mailto:Shahram_Davari@pmc-sierra.com]
> Sent: Friday, August 09, 2002 6:48 AM
> To: 'pat_thaler@agilent.com'; pkoning@equallogic.com
> Cc: ips@ece.cmu.edu
> Subject: RE: iSCSI question
> 
> 
> Pat,
> 
> Thanks for your excellent description. I now fully understand the
> issue.
> 
> However, I disagree that the text is clear on the difference between
> error recover classes and error recovery levels. As a proof, 
> look at figure 2, in section 5.15:
> 
>   +-------------------+--------------------------------------------+
>   |ErrorRecoveryLevel |  Associated Error recovery capabilities    |
>   +-------------------+--------------------------------------------+
>   |        0          |  Session recovery class                    |
>   |                   |  (Section 5.14.4 Session Recovery)         |
>   +-------------------+--------------------------------------------+
>   |        1          |  Digest failure recovery (See Note below.) |
>   +-------------------+--------------------------------------------+
>   |        2          |  Connection recovery class                 |
>   |                   |  (Section 5.14.3 Connection Recovery)      | 
>   +-------------------+--------------------------------------------+
> 
> In which, each recovery level is associated with only one 
> recovery class.
> 
> 
> Yours,
> -Shahram
> 
> > -----Original Message-----
> > From: pat_thaler@agilent.com [mailto:pat_thaler@agilent.com]
> > Sent: Thursday, August 08, 2002 5:58 PM
> > To: Shahram Davari; pkoning@equallogic.com
> > Cc: ips@ece.cmu.edu
> > Subject: RE: iSCSI question
> > 
> > 
> > Shahram,
> > 
> > There are two recovery heirarchies. You seem to be confusing 
> > error recovery level with error recovery class.
> > 
> > One is the heirarchy for implementation requirements. With 3 
> > forms of recovery, there are 8 possible combinations but to 
> > simplify interoperability and to specify minimum acceptable 
> > operation, we don't want to allow all eight. Session 
> > qualifies two ways to be level 0 of this heirarchy - it is 
> > simplest to implement and it should be able to recover from 
> > any recoverable error. 
> > 
> > Note that these are the error recovery levels that are 
> > described in 5.15. A sessions recovery level indicates the 
> > set of recovery classes it is capable of using. The recovery 
> > levels are defined such that a lower recovery level includes 
> > a subset of the recovery classes available at a higher 
> recovery level.
> > 
> > The other heirarchy is the order in which the available 
> > classes are applied once an error occurs. This is the subject 
> > of 5.14. The classes are disjoint. 
> > 
> > Once an error occurs, the device will choose an error 
> > recovery class from the set of recovery classes in its 
> > recovery level. If that recovery class fails, it may try the 
> > next higher class.
> > 
> > Error recovery level 0 includes the Session recovery class.
> > Error recovery level 1 includes the two classes useful for  
> > Digest failure recovery (Within-Command and 
> > Within-Connection) plus the Session recovery class from level 0.
> > Error recovery level 2 includes  Connection recovery class 
> > plus the classes included in level 1. 
> > 
> > I think the text already makes this clear and the pyramid 
> > correctly represents this, but perhaps the chart below the 
> > period could add "plus the capablilities of 
> > ErrorRecoveryLevel n" to the boxes for Associated Error 
> > recovery capablities for levels 1 and 2 ("n" = 0 and 1, 
> respectively).
> > 
> > I hope this helps remove some of the confusion.
> > 
> > Pat
> > 
> > -----Original Message-----
> > From: Shahram Davari [mailto:Shahram_Davari@pmc-sierra.com]
> > Sent: Thursday, August 08, 2002 2:22 PM
> > To: 'Paul Koning'
> > Cc: ips@ece.cmu.edu
> > Subject: RE: iSCSI question
> > 
> > 
> > Paul,
> > 
> > 
> > > But that's not what "hierarchy" refers to here.
> > > 
> > > The hierarchy is one of increased capability, not increased
> > > desperation.  Session recovery is the minimum required; the 
> > additional
> > > levels are optional capabilities in addition to the minimum.  Each
> > > higher level in the hierarchy is a superset of the one below.
> > 
> > It all depends on the definition of these recovery classes.
> > 
> > 1) If they are defined in a superset/subset fashion, then I agree
> > that level of complexity increases as: Session->PDU->connection.
> > Then I suggest changing texts in other parts of the draft such as
> > section 5.14 to indicate that if you have the capabilities of
> > class X, then you don't need to escalate to lower classes, because
> > class X already has those capabilities itself. Also I suggest
> > changing the hierarchy figure as following:
> > 
> > 
> >                              +
> >                             / \
> >                            / 2 \      
> >                           +-----+
> >                          /  1,2  \     
> >                         +---------+
> >                        /   0,1,2   \   
> >                       +-------------+
> > 
> > 
> > 2) If they are defined as disjoint classes, then the hierarchy for
> > complexity makes no sense. Rather you need a hierarchy for 
> escalation
> > or transition.
> > 
> > 
> > Based on the emails that I have received so far it seems that 
> > the intent is the former definition.
> > 
> > Yours,
> > -Shahram 
> > 
>