Re: iSCSI: header digest error at initiator

[Santosh Rao <santoshr@cup.hp.com>]

Matt,

My replies inline.

Regards,
Santosh

Matt Wakeley wrote:

> Santosh Rao wrote:
> >
> > If this is the intention of the recommended error recovery, it is the
> > result of not allowing score-boarding. By score-boarding an initiator
> > would detect an underrun and would just error the affected I/O back.
>
> Two comments here.  First, in your example, the initiator is inventing an
> error that really didn't occur in the target.  The target completed the I/O
> successfully, it was the transport that experienced an error, but you're
> treating it like a target error.

The LLP (initiator) would return an error to ULP indicating a transport error
(service response of "service delivery or target failure") occurred. [due to the
data underrun.]


> Second, you say that initiators and targets routinely perform scoreboarding.
> How is this done today?  Buffer(s) are provided to an I/O chip.  The I/O chip
> writes the data into the buffers.  It does not have the memory to determine
> that each and every byte has been written to. So how is the initiator/target
> supposed to be absolutely sure that every byte was written to?

The initiator would use a check along the following lines  :

(total bytes xfer'ed as indicated by the chip ) =
(no. of bytes of data xfer specified by ULP) - (resid reported by the target in
SCSI Response PDU).

to verify that all the data the target sent is accounted for at the initiator
end.




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