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RE: Re-sending a command



 
I have a question that is a slight variation to this example.
 
I->T: CmdSN=25 ITT=1 SCSI1
I->T: CmdSN=26 ITT=2 SCSI1
<time out period>
I->T: CmdSN=25 (immediate) ITT=3 TMF - LU Reset
T->I: ITT=3 ExpCmdSN=27 TMF Response - Function Complete
I->T: CmdSN=25 ITT=4 SCSI1
    The target drops the command as it falls outside its expected window.
 
Note that two commands time out and the initiator is issuing TMF (immediate) using the 1st command's Cmd SN. The target is responding with ExpCmdSN as 27 (thus acknowledging the completion of both the commands SN 25 and 26). The initiator still comes back with CmdSN as 25.
 
Question: Is the target behavior correct ? If it is, according to RFC 3720 section "3.2.2.1.  Command Numbering and Acknowledging", the initiator should update its ExpCmdSN based on the target response. So, is this also (same) initiator bug ? The initiator is MS iSCSI initiator.
 
Appreciate your answers.
Thanks
Ashish


From: Eddy Quicksall [mailto:eddy_quicksall_iVivity_iSCSI@xxxxxxxxxxx]
Sent: Thursday, August 10, 2006 3:57 AM
To: Julian Satran
Cc: ips@xxxxxxxx; Amit Kumar
Subject: Re: Re-sending a command

Thanks. I have pasted an example from Ken Sanders that is exactly the case I have seen when using the Microsoft initiator. The initiator then goes into a loop because every time it tries to reset, it sends the command again with the old CmdSN which itself causes a timeout and another reset.
 
Eddy
 
 
----- Original Message -----
Sent: Wednesday, August 09, 2006 7:42 PM
Subject: RE: Re-sending a command

Hi Eddy,
 
There's some reading between the lines needed, but if this is scenario you are describing:
 
I->T: CmdSN=25 ITT=1 SCSI1
<time out period>
I->T: CmdSN=26 (immediate) ITT=2 TMF - LU Reset
T->I: ITT=2 ExpCmdSN=26 TMF Response - Function Complete
I->T: CmdSN=25 ITT=1 SCSI1
 
In this case, the target actions for the TMF - LU Reset will ensure that no responses will be sent for the affected commands (including CmdSN=25) after the TMF response is sent.
 
The initiator is in effect (re)sending a command outside the CmdSN window, and a working target will discard it.
 
HTH
Ken
----- Original Message -----
Sent: Thursday, August 10, 2006 2:22 AM
Subject: Re: Re-sending a command


Eddy,

The LU reset "plugs the holes" in command sequence and the old CmdSN should not be used (it is definitely an initiator bug). If you have seen it Mallikarjun may want to mention that dropping the command is the expected behavior of the target after all the task management commands that "plug the holes" in the implementation guide.

Julo


"Eddy Quicksall" <eddy_quicksall_iVivity_iSCSI@xxxxxxxxxxx>

10/08/06 01:34

To
<ips@xxxxxxxx>
cc
Amit Kumar <Amit_Kumar@xxxxxxxxxxx>
Subject
Re-sending a command





It was brought to my attention that one initiator being tested will re-issue a "timed out" command using the same CmdSN after it has issued a LU Reset. When this happens the command is dropped. Note that this is on a single connection session.
 
I'm wondering if this could be an initiator bug or if there is a case where it is actually valid (in the report I have I don't know if the initiator also reissued the command with a valid CmdSN or not).
 
Does anyone know?
 
Eddy_______________________________________________
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