Re: iSCSI: header digest error at initiator

[julian_satran@il.ibm.com]

Santosh,

In the SCSI world there is no scoreboarding at the initiator.

The whole operation is master-slave with the target being the master.
The status, counters etc. are determined by the target and the initiator
has propagate them to the application client.

Julo

Santosh Rao <santoshr@cup.hp.com> on 16/01/2001 22:42:47

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

To:   IPS Reflector <ips@ece.cmu.edu>
cc:
Subject:  Re: iSCSI: header digest error at initiator




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.