Re: Receiving a SCSI response after abort task was sent

"Eddy Quicksall" <[email protected]> Sun, 9 Jul 2006 13:35:42 -0400

Newsgroups	gmane.ietf.ips
Message-ID	<[email protected]>

Wasn't Bob talking about technologies other than iSCSI?

Bob, are you sure? Do you have an example of such a technology?

I would think it would be dangerous for a technology to allow a SCSI response to be received after the TMF response has been received for the same command. My reasoning is that once the initiator has received the TMF response it can reuse the ITT. In that case if the SCSI response for the aborted command comes after the TMF response for the same command but a new command has already used the same ITT, then there would be no way to determine that the response should be discarded.

Eddy
----- Original Message -----
From: William Studenmund
To: Robert Snively
Cc: [email protected] ; [email protected]
Sent: Wednesday, July 05, 2006 1:47 PM
Subject: Re: [Ips] 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

------------------------------------------------------------------------------

_______________________________________________
Ips mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/ips