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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
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 "
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