GFRAZIER at ausvm6.vnet.ibm.com GFRAZIER at ausvm6.vnet.ibm.com
Mon Aug 1 13:59:15 PDT 1994

In the continuing discussion about FCP recovery aborts, consider
the following potential solution.

If FCP allows an initiator to wait RA_TOV before reusing an XID
as an alternative to requiring targets/initiators to abort
ambiguous exchanges, AND if RA_TOV is set for *zero* (for nondelaying
fabrics) or to the loop circuit time (on a loop), then perhaps
we have a solution which allows the optimization which Kurt needs
for the loop.

                            Giles Frazier
                            gfrazier at ausvm6.vnet.ibm.com
                            IBM Austin

**********LEASE RECENTLY WRITTEN REFERENCED NOTE************************

 | The way I look at it is as follows: In class 1 and 2,
 | potentially hundreds of ABTS/LS operations do not need to be done if
 | FCP remains unchaged. This is because a very large number of exchanges
 | may exist but a very small number of sequences may be ambiguous at the
 | target. (Please refer to FCP 8b for definition of ambiguous.)
 | This situation occurs when the initiator has a very
 | large number of commands (open exchanges) at the target but the target
 | only has a single ambiguous exchange. (e.g. one of the exchanges has
 | an unacknowledged frame but all the rest of the exchanges are
 | quiescient--the target has acknowledged the command but is accessing
 | the data.)

 I agree with Giles on this point.  There are interlock points where
 one side owns Sequence Initiative and the other side knows it owns it.
 If a Task Management flag is received (or a Unit Attention condition
 established) at these points, no Recovery Abort is needed.  In class
 3, three out of the 7 possible Sequence launch points fall into this
 category as noted by my previous memo.

 This is a SEPARATE issue from whether or not Targets are required to
 initiate ABTS for all the other cases where the Exchange is "ambiguous".

 | There is another solution which may pertain more to class 3 but could
 | also be used: The initiator may wait RA_TOV before reusing any of the
 | XID's.
 | This may be the only reliable method for class 3 anyway.

 Not true.  Class 3 local loops or fabrics which cannot delay frames do
 not require the N_Ports to wait R_A_TOV - the behavior is identical to
 class 1 in such cases.  FCP should not rule out optimizations for
 these topologies.
*********************END OF REFERENCED NOTE

More information about the T10 mailing list