FCP-2: Lost Write Data, Not Last Frame of Sequence, Unacknowledged classes.

Santosh Rao santoshr at cup.hp.com
Tue Jun 25 17:18:25 PDT 2002

* From the T10 Reflector (t10 at t10.org), posted by:
* Santosh Rao <santoshr at cup.hp.com>

We have a question regarding Annexe C Figure C.15 of FCP-2 Rev 07a. This
figure depicts the FCP-2 SLER (sequence level error recovery) for the
case of a lost write data iu which is not the last frame in the sequence
for an un-acknowledged class.

The figure shows the recovery as :
"Wait REC_TOV. If FCP_DATA is returned, continue with the exchange.
Otherwise, perform error recovery".

Are the above statements referring to the actions to be taken by the
initiator or the target ? Since this is a write operation, it is not
clear how FCP_DATA could be returned to the initiator. (?)

Since the last frame of the sequence is assumed to have made it to the
target (lost write data iu was not the last frame of sequence), the
target has the sequence initiative and can complete the exchange with a
FCP_RSP indicating a CHECK CONDITION status with appropriate sk/asc/ascq
(as per Section 9.4.1). In this case, is the initiator expected to look
for CHECK CONDITION command completions of certain sk/asc/ascq
combinations and initiate a SLER operation on seeing those ? What
specific sk/asc/ascq combinations should the initiator look for while
parsing command completions to initiate SLER ?

If this is not done, a write underrun condition as described above
cannot be recovered from, since SLER will not kick in and the
ULP/application will see the error.

Can someone clarify what is the error recovery actions taken by the
initiator and target in this situation ?

Santosh Rao

The world is so fast that there are days when the person who says 
it can't be done is interrupted by the person who is doing it.
	~ Anon
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