|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI questionit is alredy in - julo
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 >
Home Last updated: Fri Aug 09 18:18:55 2002 11598 messages in chronological order |