FCP_RSP Residual Checking.

Santosh Rao santoshr at cup.hp.com
Thu Jul 5 12:15:21 PDT 2001

* From the T10 Reflector (t10 at t10.org), posted by:
* Santosh Rao <santoshr at cup.hp.com>
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I've got a question on target behaviour while sending a CHECK CONDITION
SCSI status in its FCP_RSP IU.

Is the target required to initialize the fields FCP_RESID_UNDER,
FCP_RESID_OVER & FCP_RESID when any I/O is completed without the data
phase having transferred exactly FCP_DL bytes, regardless of the SCSI
Status being returned ? 

When the target generates a CHECK CONDITION on an I/O and may have
returned less than FCP_DL bytes in the data phase for that I/O, is it
required to set the FCP_RESID_UNDER to 1 and indicate the number of
bytes not transferred in the FCP_RESID field?

FC-PLDA Section states that :
"SCSI targets that transfer less than FCP_DL bytes during the FCP_DATA
IUs shall set the FCP_RESID_UNDER to 1". 

No exceptions are specified in the case of a CHECK CONDITION in the
above definition, implying that FCP_RSP residual checking can be
performed irrespective of the SCSI Status that was returned in the

However, the wording descriptions of FCP_RESID_UNDER, FCP_RESID_OVER &
FCP_RESID in SCSI-FCP & FCP-2 are not as stringent as FC-PLDA and do not
mandate that FCP_RESID_UNDER shall be set when the data transferred is <

What is the behaviour initiators can expect under the above condition ?
Is there a conflict in the behaviours described by FCP/FCP-2 & FC-PLDA ? 

Santosh Rao

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