RE: sector alignment for DataOut PDUs?

["Julian Satran" <Julian_Satran@il.ibm.com>]

It reffers explicitely (and with good reason) to unsolicited data ONLY.
See the archives for a reason.
Solicited bursts are what the target asks through R2T.

Julo

Paul Koning <ni1d@arrl.net> 28-02-02 16:40

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        ips@ece.cmu.edu         Subject:        RE: sector alignment for DataOut PDUs?

>>>>> "Julian" == Julian Satran <Julian_Satran@il.ibm.com> writes:

 Julian> Where is the hint you are alluding to? 

 >> ....  (It does
 >> hint that targets may object if you don't do it that way --
 >> which makes no sense at all unless there's a MUST for
 >> initiators to do what targets are allowed to expect.)

In this section:

     9.5  Unsolicited Data and Performance

        Unsolicited data on write are meant to reduce the effect 
        of latency on throughput (no R2T is needed to start send-
        ing data).  In addition, immediate data are meant to 
        reduce the protocol overhead (both bandwidth and execu-
        tion time).

        However, negotiating an amount of unsolicited data for 
        writes and sending less than the negotiated amount when 
        the total data amount to be sent by a command is larger 
        than the negotiated amount may negatively impact perfor-
        mance and may not be supported by all the targets.

Specifically, the last sentence.  That statement is not a good thing,
because it explicitly permits failures to interoperate, which a
protocol standard must never do.  Instead, a receiver must always be
required to accept anything that the standard permits the sender to
send in a state that the sender can legitimately get to. 

There are two ways to fix this: one is to forbid the sender sending
less than the negotiated unsolicited data length.  The other is to
require the receiver to accept unsolicited data of less than the
negotiated length.  Either change works because either change
establishes interoperability.

                     paul