Subject: iSCSI: FirstBurstSize, etc

From: "Eddy Quicksall" <[email-masked]>
Date: Thu, 11 Oct 2001 16:22:50 -0400

I am wondering about the following statement:

  FirstBurstSize MUST NOT exceed MaximumBurstSize.

It doesn't seem to fit the various definitions. I made the following diagram
from the definitions and FirstBurstSize came out larger then MaxBurstSize.

Here are the definitions I am going by:

25 FirstBurstSize
 Initiator and target negotiate the maximum amount of unsolicited data
 an iSCSI initiator may send to the target, during the execution of a
 single SCSI command, in units of 512 bytes.

24 MaxBurstSize
 Initiator and target negotiate maximum SCSI data payload in an iSCSI
 sequence (a sequence of Data-In or Data-Out PDUs ending with a Data-In
 or Data-Out PDU with the F bit set to one) in units of 512 bytes.

I get the definition of a sequence from "2.2.2.3 Data Sequencing":

 For output data PDUs, DataSN starts with 0 for the first data PDU of a
 sequence (the initial unsolicited sequence or any data PDU sequence
 issued to satisfy an R2T) and advances by 1 for each subsequent data
 PDU.

         |<------------------ Unsolicited data ------------------->|
         |                    |<------------ Sequence ------------>|
|Command | Immediate Data  |  |<---- Remaining unsolicited ------->|
|========|=================|  |================|  |F===============|
         |<-DataPDULength->|  | DataPDULength  |  | DataPDULength  |
                              |<--------- MaxBurstSize ----------->|
         |<------------------- FirstBurstSize -------------------->|

[email-masked]

---

From: Santosh Rao <[email-masked]>
Date: Thu, 11 Oct 2001 14:15:35 -0700

Julian,

I believe the definition of an outbound data sequence must be modified
to factor in the initial immediate data sent in the scsi command pdu.
The current definition of an outbound data sequence implies that it
starts from a data-out pdu and therefore, excludes the immediate data
component.

As a result, Eddy's diagram shows FirstBurstSize to be > MaxBurstSize,
since the data sequence does not include the immediate data.

- Santosh

-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : [email-masked]
Phone : 408-447-3751
##################################