RE: iscsi: unsolicited data question

["Julian Satran" <Julian_Satran@il.ibm.com>]

Yes the F bit in Data is not strictly needed except to simplify target function, recovery and bidirectional command execution.
Initiators may send data out-of-order (parameters control this and this might be needed in special circumstances - e.g., copy a disk to tape) and a target might have trouble keeping track of what it got or not (discarded PDUs due to errors make the picture even more complex). The F bit is a simple indication that says "that's it"!

Julo

Dennis Young <dyoung@rhapsodynetworks.com> 06/13/2002 08:02 PM Please respond to Dennis Young

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        ips@ece.cmu.edu, owner-ips@ece.cmu.edu         Subject:        RE: iscsi: unsolicited data question

I think you are refering to the F bit in the SCSI Write.  I was talking about the F bit in the Data-out.
Please confirm.
Thanks,
Dennis
-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Thursday, June 13, 2002 6:18 AM
To: Dennis Young
Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: RE: iscsi: unsolicited data question


Not exactly - an initiator may decide to send only non immediate or only immediate in the first case the absence of F is the sign of things to come and in the later F indicates nothing will come. The later is allowed. 

Julo

Dennis Young <dyoung@rhapsodynetworks.com> 06/13/2002 04:00 AM Please respond to Dennis Young

To:        Julian Satran/Haifa/IBM@IBMIL        cc:        ips@ece.cmu.edu, owner-ips@ece.cmu.edu        Subject:        RE: iscsi: unsolicited data question

Thanks to yours and others' explanation, now I am more clear, but I have 
another question: 
  
Based on your reply, and let me emphasize it by repeating the 4th paragraph 
on page 42 of draft 12-98: 
    "... If any non-immediate unsolicited data are sent, the total unsolicited 
    data MUST be either the negotiated amount or all the data if the total 
    amount is less than the negotiated amount for unsolicited data. ..." 
  
With this rule, do we still need the F bit in the Data-out (both for the solicited 
and unsolicited Data-out)?  The F bit seems redundant since the target has 
enough information to figure out the final unsolicited Data-out and the final 
solicited Data-out (based on the FirstBurstSize, Offset and DataSegmentLength 
in the Data-out, and the ExpectedDataTransferLength in the corresponding 
SCSI Write PDU). 
  
Thanks, 
Dennis 
  
-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Wednesday, June 12, 2002 11:21 AM
To: Dennis Young
Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: RE: iscsi: unsolicited data question


You are wrong about waiting - read my previous text. 
You need unsolicited as the amount in one PDU may not be all you want. 

Julo

Dennis Young <dyoung@rhapsodynetworks.com> Sent by: owner-ips@ece.cmu.edu 06/12/2002 08:49 PM Please respond to Dennis Young

To:        Julian Satran/Haifa/IBM@IBMIL       cc:        ips@ece.cmu.edu, owner-ips@ece.cmu.edu       Subject:        RE: iscsi: unsolicited data question

Are you saying that, for a session that has InitialR2T=No in effect, the initiator 
must send all its data as unsolicited first, up to the amount negotiated in 
FirstBurstSize, before it waits for a R2T from the target? 
 
Can you shed some light on why we need unsolicited Data-out PDU when there 
is ImmediateData, seems like they both serve the same purpose, having both of 
them only make the spec more complex. 
 
Thanks, 
-Dennis 
 
-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Wednesday, June 12, 2002 10:19 AM
To: Dennis Young
Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: RE: iscsi: unsolicited data question


This is the reason why the initiator is required to send ALL unsolicited data (target can count on it and start sending R2Ts as soon as it sees the first header> 
Neither bandwidth nor latency are wasted. 

Julo

Dennis Young <dyoung@rhapsodynetworks.com> 06/12/2002 08:05 PM Please respond to Dennis Young

To:        Julian Satran/Haifa/IBM@IBMIL      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 "