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RE: iSCSI: FirstBurstSize and unsolicited data
In an earlier EMAIL
this morning, I said "I think something should be said. It can be short and
sweat."
But, I did not
notice that -14 is now the final draft. So, forget what I
said.
Eddy
Pat,
Do you think we should
make the position of the initial data expliciit (i.e., add text) where this
seems obvious?
Julo
| pat_thaler@agilent.com
06/25/2002 02:30 AM Please respond to pat_thaler
| To:
rsnively@brocade.com, pat_thaler@agilent.com,
nramamur@npd.hcltech.com, Julian Satran/Haifa/IBM@IBMIL cc:
ips@ece.cmu.edu Subject:
RE: iSCSI: FirstBurstSize and unsolicited data
|
Robert,
I think there should be a restriction but it isn't
as broad as requiring DataSequenceInOrder = Yes. The necessary and sufficient requirements are (I think):
When immediate data is sent, it MUST begin with the first byte of the
data transfer - rationale:
there is no mechanism such as DataSN in the SCSI Command PDU to indicate
position of the immediate data so it must have an implied position.
When unsolicited non-immediate data is sent, there is an implied R2T
for the first n bytes of data
where n = min(Expected Data Transfer Length, FirstBurstSize)
This implied R2T is to be satisfied by the
immediate data plus unsolicited SCSI Data-out PDUs. As above, any immediate
data must begin with the first byte of the data transfer. If
DataSequenceInOrder=No, then the data in the unsolicited SCSI Data-out PDUs
MAY be in any order but MUST be the bytes that satisfy the implied R2T (that
is, the first n bytes of the data). rationale: Since the R2T is implied, it doesn't have an explicit
position and must have an implicit position. I
don't think these requirements are articulated in the draft. Pat
-----Original Message----- From: Robert
Snively [mailto:rsnively@brocade.com] Sent: Monday, June 24, 2002
2:30 PM To: 'THALER,PAT (A-Roseville,ex1)'; Nandakumar Ramamurthy;
Julian Satran Cc: ips@ece.cmu.edu Subject: RE: iSCSI:
FirstBurstSize and unsolicited data
I must have missed something in the document. I did not
see any restriction that
required EMDP = 0 (or in iSCSI-ese, DataSequenceInOrder = yes)
when immediate data was transmitted.
I would have expected such a requirement. If that is not the case, then any data can be
transmitted first and any data
can be requested with the first (overlapping) R2T, somewhat confusing
the issue. If someone can point me to that restriction, I would be
delighted.
Bob -----Original Message----- From: THALER,PAT (A-Roseville,ex1)
[mailto:pat_thaler@agilent.com] Sent: Friday, June 21, 2002 9:46
AM To: Nandakumar Ramamurthy; Julian Satran Cc:
ips@ece.cmu.edu Subject: RE: iSCSI: FirstBurstSize and unsolicited
data
Nandakumar, There
are no restrictions on the amount of immediate data sent other than that it
must be less than MaxRecvDataSegmentLength and less than FirstBurstSize. So in
the conditions you have chosen, the initiator could send any amount of
ImmediateData from 4 Bytes to 8 KB. Doing so should not cause an error at the
target. The purpose of allowing an implicit InitialR2T is to gain
efficiency by letting data start flowing without having to wait a round-trip
delay for an R2T. Gaining this efficiency requires that the target know how
much unsolicited data will be sent when it receives the SCSI Command PDU so
that it can immediately send the first explicit R2T. The rule on sending the
full FirstBurstSize (or all the data) when unsolicited data is sent in
Data-out PDUs achieves this. When the target sees the SCSI Command PDU with
the F bit set to 0, it knows that the first data it needs to request with an
R2T starts after FirstBurstSize bytes. When the SCSI Command PDU has
an F bit set to 1, then the target knows that DataSegmentLength is the amound
of unsolicited data being sent and it can construct its first R2T. Therefore
there is no reason to restrict the amount of unsolicited data sent when only
immediate data is sent (other than that it not exceed the maximums).
That is what is reflected in the rules. Pat
-----Original Message----- From:
Nandakumar Ramamurthy [mailto:nramamur@npd.hcltech.com] Sent:
Friday, June 21, 2002 1:36 AM To: Julian Satran Cc:
ips@ece.cmu.edu Subject: Re: iSCSI: FirstBurstSize and unsolicited
data
Hi, I have
been following the discussion on this thread. I
still have certain doubts regarding the conditions I specified in my original mail. The
conditions are :
FirstBurstSize = 64KB EDTL = 100KB ( EDTL > FirstBurstSize) MaxRecvDataSegmentLength = 8KB ImmediateData = Yes InitialR2T =
Yes In the above case the initiator cannot send unsolicited
Data-out PDUs. Here unsolicited
data(ImmediateData) < FirstBurstSize. Will the target report any
error in this case? The modified text for Section 9.4.6.2 only refers to the
cases where unsolicited Data-outs can be
sent. Please clarify if I am missing something very
obvious.
Thanks, Nandakumar Member
Technical Staff HCL Technologies, Chennai, INDIA. http://san.hcltech.com
----- Original Message ----- From: Julian Satran To: Eddy Quicksall Cc: ips@ece.cmu.edu
Sent: Friday, June 21,
2002 11:41 AM Subject:
RE: iSCSI: FirstBurstSize and unsolicited data
Eddy,
I assume you meant EDTL not DSL
and then the answer is yes and I again forgot to subtract the immediate.
A better formulation would be:
The target reports the
"Incorrect amount of data" condition if dur-ing data output the total data
length to output is greater than First-BurstSize and the initiator sent
unsolicited non-immediate data but the total amount of unsolicited data is
different than FirstBurst-Size. The target reports the same error when the
amount of data sent as a reply to an R2T does not match the amount
requested.
Julo
| "Eddy Quicksall"
<Eddy@Quicksall.com>
06/21/2002 12:22 AM Please respond to "Eddy Quicksall"
|
To:
Julian Satran/Haifa/IBM@IBMIL cc:
Subject:
RE: iSCSI: FirstBurstSize and unsolicited
data
|
Isn't this saying
that if DSL > FirstBurstSize, it would be incorrect to send non-immediate
unsolicited which is not equal to FirstBurstSize? The target reports the "Incorrect amount of data" condition if
dur-ing data output the total data length to output is greater than
First-BurstSize, but the initiator sent an amount different than
FirstBurstSize of unsolicited non-immediate data or the amount of data sent as
a reply to an R2T does not match the amount requested. Eddy
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