Re: iSCSI : digest error handling violates EMDP/InDataOrder

[julian_satran@il.ibm.com]

Santosh,

The bit and the interpretation are protocol specific.

FCP uses it like iSCSI - i.e. the order has to maintained within a sequence
(a R2T derived output or the entire input).
In that sense we are not violating the EMDP.

And BTW the recovery procedure in FCP is similar although a bit more
complicated than ours and involves also
a link level sequence.

Julo



Santosh Rao <santoshr@cup.hp.com> on 13/04/2001 03:54:28

Please respond to Santosh Rao <santoshr@cup.hp.com>

To:   IPS Reflector <ips@ece.cmu.edu>
cc:
Subject:  iSCSI : digest error handling violates EMDP/InDataOrder




Where :
=======

Section 6.2 (pg 80). Digest Errors
-----------------------------------
"If the error is a Data-Digest-Error in a Data-PDU, the target MUST
either request retransmission with a R2T or answer with a Reject iSCSI
PDU and abort the task."

Problem :
---------
On a Data digest error detected by a target, it MUST NOT request
re-transmission of the data PDU thru an R2T if the session login key
InDataOrder is set to yes. The current rev 05 draft violates
InDataOrder/EMDP settings by allowing a re-transmission of R2T by
target.

Scenario :
==========
initiator           target
---------           ------
EMDP=0
InDataOrder=YES
(exp_off=0)
        offset=0,len=64k <------ R2T

--------> data PDUs
(exp_off = 64K)
                              data digest error results in
                     an 8K PDU being dropped at offset 24K.

       offset=24K,len=8K  <------ R2T for missing PDU.

exp_off != offset


- Santosh