Subject: RE: iSCSI: data and data sequences for Read

From: "Lakshmi Ramasubramanian" <[email-masked]>
Date: Tue, 13 Nov 2001 17:02:14 -0800

MaxBurstSize applies both to the initiator and the target. When
initiator
sends data (WRITE) it limits the sequence to MaxBurstSize. Initiator
does not
require R2T for READ because when it issues read, it is assumed that it
is ready
to receive data. Also, the maximum read size it's going to request from
target is
MaxBurstSize.

Is that right or am I missing something?

 -lakshmi

-----Original Message-----
From: Paul Koning [mailto:[email-masked]] 
Sent: Tuesday, November 13, 2001 2:22 PM
To: [email-masked]
Subject: iSCSI: data and data sequences for Read

I hope this isn't a dumb question, but between the -08 spec and the
archives I'm puzzled about the details around data sequences in the
case of Read operations.

As far as I can tell, a read can result in one or more data sequences
coming back.  These are numbered with DataSN values that  keep going
up across sequence boundaries.  Each sequence is limited by
MaxBurstSize, but the total Read size (sum of all the sequences) is
not bounded other than by SCSI.

In the Write case, something analogous happens but there there's an
R2T to control the flow of data sequences.  

As far as I can see, there is nothing analogous in the Read case.  In
other words, while MaxBurstSize limits the size of a data sequence,
there is no mechanism limiting the number of bursts, or the rate at
which you send back DatIn PDUs (other than TCP window control).

Is that right or did I miss something?  If it's right, what is the
purpose of having the notion of a Data Sequence for DataIn, and what
does MaxBurstSize do for you in that case?

Thanks,
	paul

---

From: Santosh Rao <[email-masked]>
Date: Wed, 14 Nov 2001 09:35:28 -0800

Lakshmi Ramasubramanian wrote:
> sends data (WRITE) it limits the sequence to MaxBurstSize.

I don't believe it is the initiator's responsibility to chunk outbound
data sequences into MaxBurstSize chunks. It is the target's
responsibility to ensure that it does not request > 'MaxBurstSize' bytes
of data in any R2T that it issues. 

- Santosh

> Initiator

-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : [email-masked]
Phone : 408-447-3751
##################################