RE: iscsi: unsolicited data question

[pat_thaler@agilent.com]

Dennis,

 

The target can tell from the command whether there will be unsolicited data or not. bit 0 of the Flags and Task Attributes field ( the F bit) in the SCSI Command PDU is 1 if there are no unsolicited Data-Out PDUs. Also, if there is unsolicited data, the amount of unsolicited data sent is the lesser of the data transfer length or FirstBurstSize so if bit 0 indicates unsolicited data will be sent, the target knows where its first R2T will start.

 

Pat

 

 

-----Original Message-----
From: Dennis Young [mailto:dyoung@rhapsodynetworks.com]
Sent: Wednesday, June 12, 2002 10:05 AM
To: 'Julian Satran'
Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: RE: iscsi: unsolicited data question

Julian,

 

This leads me to a more interesting question.

A session with InitialR2T=No in effect, i.e. unsolicited Data-out

allowed, could cause unintended waste of bandwidth, depending on

how fast the target sends our R2T in response to the SCSI Write.

 

If the target sees the unsolicited Data-out PDU before building the

R2T, then everything is fine. 

If the target doesn't see the unsolicited Data-out PDU before building

the R2T, the R2T would request the same portion of data in the

unsolicited Data-out, thus bandwidth is wasted.

 

The question is, how can a target be smart about this?

Should the target wait a moment for the possible unsolicited Data-out

after receiving each SCSI Write, this sounds kludgy.

 

Also, why do we need the unsolicited Data-out PDU feature when

there is ImmediateData?

 

Regards,

Dennis

 

-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Wednesday, June 12, 2002 6:05 AM
To: Dennis Young
Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: Re: iscsi: unsolicited data question

yes - julo

Dennis Young <dyoung@rhapsodynetworks.com> Sent by: owner-ips@ece.cmu.edu 06/12/2002 06:20 AM Please respond to Dennis Young

To:        ips@ece.cmu.edu         cc:                 Subject:        iscsi: unsolicited data question

I have a question which has been asked before, but I couldn't find a direct
answer in the archive.  The table on page 200 of draft 12 doesn't directly
answer this question either.

The first paragraph on page 36 of draft 12 says "Targets operate in either
solicitied (R2T) data mode or unsolicited (non R2T) data mode."
tells me that a target, at all times during a data sequence transfer, can be

one or the other, but not both (non R2T for the initial data out, R2T for
the
remaining data).  Is this correct?

Thanks,
Dennis

---snip from an old email dated 3/30/2001---

" Hi Julian
Sorry if I'm covering old ground... Is it possible to use unsolicited data
for the first burst and then request any remaining data using R2T? For
example, if the target has a previously allocated buffer available (length
defined by FirstBurstSize) for unsolicited data, then once the initiator has
sent unsolicited data up to and including this amount then the remaining
data (if any) can be requested using R2T once the target has the buffer
space available.
...Matthew Burbridge Hewlett Packard, Bristol Telnet: 312 7010 E-mail:
matthewb@bri.hp.com "