Re: Receiving a SCSI response after abort task was sent

On Jul 3, 2006, at 10:18 AM, Robert Snively wrote:

> With one minor warning, I agree with David.
>
> Warning below:
>
> > Is the host that issued the abort task willing to receive a SCSI  
> response for that task?
> > Is it willing to receive only a task management response for the  
> abort task?
>
> Yes and No in that order, the SCSI response is possible and must be
> handled.  There will always be a task management response, independent
> of whether the SCSI response is issued.  One important rule is that
> the SCSI response cannot occur *after* the task management response.
>
> In some technologies and under some conditions, it is  
> hypothetically possible for a SCSI
> response to appear at an initiator after the task management  
> response.  In such environments, this will
> be detected as a SCSI response for which there is no SCSI request  
> and it will be discarded.
> Since TCP/IP forces in-order behavior on the SCSI stream, and since  
> the abort task is
> normally sent through the same stream as the command, this normally  
> may be ignored
> by iSCSI.

I don't think this is a concern, because the ABORT TASK MUST be on  
the same connection (section 10.5.1, page 131 of RFC 3720) as the  
command in question. Thus StatSN numbering for the two is in the same  
number space. The SCSI response should have a lower StatSN than the  
TMF response as StatSN is the only real way to determine what is  
"before" or "after", and we are talking about the case where the task  
finished "before" the abort.

So as the initiator processes StatSN responses, it will see the SCSI  
response "before" the TMF response.

As long as any other iSCSI transport (other than TCP) retains StatSN,  
this will work right.

Take care,

Bill

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