RE: iSCSI: FirstBurstSize and unsolicited data

[Robert Snively <rsnively@Brocade.COM>]

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