Re: iSCSI: data and data sequences for Read

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

Lakshmi Ramasubramanian wrote:
> 
> MaxBurstSize applies both to the initiator and the target. When
> initiator
> 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
> 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:ni1d@arrl.net]
> Sent: Tuesday, November 13, 2001 2:22 PM
> To: ips@ece.cmu.edu
> 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

-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
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