Re: Read data chunk size and segmentation negotiation

[Mark Burton <markb@ordern.com>]

From: julian_satran@il.ibm.com
Subject: Re: Read data chunk size and segmentation negotiation
Date: Thu, 23 Nov 2000 15:56:40 +0200

> Interesting questions - but why?
> 
> Why should the initiator care about the chunks (it has already reserved the
> memory when issuing the read) and about how many - the target is going to
> tell him when it is over by the Status or Response.
> 
> Could you elaborate?
> 

I understand from your response that it is an (implicit) requirement
that all initiators must always accept a data response of any length
up to the expected data transfer length. This is logical because it is
the initiator that specifies the expected data transfer length.

I just wonder if there is (or will be) any situation that would
require the size of the data responses to be limited by the initiator
whilst still allowing for a larger data transfer length. If no such
situation can ever occur then the negotiation is not required.

However, I would still prefer that the implicit requirement that an
initiator must be capable of accepting all of the read data in one
response to be stated explicitly.

Furthermore, unless I am mistaken, the draft standard does not
explicitly state that initiators must be able to accept read data that
has been segmented into multiple responses (as opposed to a single
data response). I would also prefer that this requirement is stated
explicitly. As background to this, I am aware of an initiator
implementation that cannot accept segmented read data. Whether it was
done deliberately or by accident I don't know.

I just feel that the the more loose ends that are nailed down, the
greater the chance that the resulting end products will be
interoperable.

Regards,

Mark

----------------

> 
> Folks,
> 
> Given the definition of the SCSI Data Response format in Section 2.8
> and the example in Appendix B of draft-ietf-ips-iscsi-01.txt it
> appears necessary for the initiator and the target to agree on the
> maximum amount of data that can be sent in a single SCSI Data
> response.
> 
> Another issue is that either the initiator should be required to
> accept multiple data responses containing the content for a single
> read or it should have some means of informing the target that it will
> not accept multiple data responses per read i.e. the read data must
> not be segmented.
> 
> I guess additional login keys could be added to negotiate these
> constraints.
> 
> Regards,
> 
> Mark
> 
> 
> 
> 
> 
>