Re: iSCSI: error recovery

["Mallikarjun C." <cbm@rose.hp.com>]

>> At command restart it will resent what it has.
>
>No, command retry (restart) was meant to retry the whole I/O.  It was not meant
>to be "send what you think I didn't get".

Yes, I agree.  This is the way I understand the spec as well.  

Julian, could you please clarify the following:

o You stated that R2T is the exclusive means used by a target to 
  request partial data xfers on retried writes.  How then is the CmdRN
  (would be DataRN) in a Write data payload used?  It seems redundant 
  to me.

o Underflow, overflow and residual count in a SCSI response PDU
  must reflect the status taking into account the retry bit and
  the partial data xfers if any.  Is this a correct interpretaion?


>> Again, in the interests of simplicity, I request that data overlay be
>> forbidden.  Period.  Otherwise, the initiator would have to perform score
>> boarding at the byte level to be positively sure that each byte was really
>> received.
>> /<JS>
>> That is an interesting point.  I would argue that in the interest of
>> simplicity
>> we will stay neutral.  If we explicitely forbid it the every Initiator is
>> bound to check (enforce) it and that is a lot of work.  I assume we will want
>> to
>> use SHOULD.  My point about scoreboarding is that initiators are not required
>>
>> to check (enforce) the overlap.
>
>I disagree Julian.  Forbidding a target from performing a function does not
>mandate that the initiator play policeman and verify that the target is not
>doing what it's forbidden to do.
>
>If we do not forbid it, then the initiator will have to support it, and that
>would be a lot of work.

I second Matt.  I would contend that even a target (supporting data overlay)
complexity is significantly higher to keep track of the "net" amount of data
that it sent out at any moment.  Data overlay only seems to increase complexity
at either end in addition to consuming network bandwidth.
--
Mallikarjun 
M/S 5601			
Networked Storage Architecture
HP Storage Organization
Hewlett-Packard, Roseville.
cbm@rose.hp.com