iSCSI: MaxRecvPDULength simplification

[Michael Schoberg <michael_schoberg@cnt.com>]

I've looked over some of the reflector messages regarding MaxRecvPDULength negotiation (back to Oct 2001).  I can't find the discussion of why this value must be available for negotiation outside of login.  It really complicates SNACK and Task Reassignment if the initiator can change this value on-the-fly.  Would it be too restrictive to propose the following rules?

 

1) MaxRecvPDULength is negotiated only at login before FFP.

 

2) For message-level recovery, a connection must be prepared to accept the MaxRecvPDULength of the connection it's providing fail over capability for.  It doesn't seem unreasonable to expect fault tolerant configurations to comply with this.  It would simply be stating that RecoveryLevel 2 devices should be somewhat matched in this capability.

 

 

 

 -----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Tuesday, March 26, 2002 1:50 AM
To: Michael Schoberg
Cc: IPS Reflector (E-mail); owner-ips@ece.cmu.edu
Subject: Re: iSCSI: SNACK RunLength

Michael,

The paragraph says that if you issue a SNACK after the MaxPDURecvLength has decreased you should use RunLength 0 (meaning all) instead of a specific runlength which might not be accurate anymore.

Julo

Michael Schoberg <michael_schoberg@cnt.com> Sent by: owner-ips@ece.cmu.edu 25-03-02 19:43 Please respond to Michael Schoberg

To:        "IPS Reflector (E-mail)" <ips@ece.cmu.edu>         cc:                 Subject:        iSCSI: SNACK RunLength

Am I just not reading this or can this paragraph use some help?  Can someone
give an interpretation?

  9.16.3  RunLength
                                 ...

          The first data SNACK, issued after initiator's MaxRecvPDULength
          decreased, for a command issued on the same connection before the

          change in MaxRecvPDULength, MUST use RunLength "0" to request
          retransmission of any number of PDUs (including one).  The number
of
          retransmitted PDUs in this case, may or may not be the same as
the
          original transmission, depending on whether loss was before or
after
          the MaxRecvPDULength was changed at the target.


Does this refer to something like:

For connections with unacknowledged PDUs that undergo MaxRecvPDULength
negotiation ...