Subject: Re: [iSCSI] Resolution of management commands and multiple head of queue commands.

From: "Julian Satran" <[email-masked]>
Date: Mon, 6 Aug 2001 19:53:56 +0300

Immediate commands don't just get discarded - they are rejected.

Julo

"Douglas Otis" <[email-masked]>@ece.cmu.edu on 06-08-2001 16:57:42

Please respond to "Douglas Otis" <[email-masked]>

Sent by:  [email-masked]

To:   "Ips" <[email-masked]>
cc:
Subject:  [iSCSI] Resolution of management commands and multiple head of
      queue commands.

All,

iSCSI version .7 is a significant improvement.  Two areas that prompted a
draft still seem unresolved.  Section 8.1 mentions a potential problem
without addressing at least a suggested means of handling these situations.
There are management commands that can not resolve with connection
allegiance alone.  On another point, with no assurance or direct
confirmation of Immediate Delivery Commands (IDC) and the potential for
only
a single command resource being allocated by the target, one must wonder
how
these commands are to be handled in practice.  Preventing more than a
single
command to be sent as IDC would be one solution as there is assurance there
will be resources for only a single command.  If this were to be adopted as
the method of handling these IDC commands, then such a flag could serve to
allow an exception to the command window limit and avoid creating an
overlaid command sequence count that then only serves to befuddle
acknowledgement.  If multiple IDC commands need to be sent, then either
waiting for acknowledgement or sending these commands consecutively where
acknowledgement would indicate quickly status of these commands without the
initiator pondering their status at a point in time where speed of
resolution is important.

Doug

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From: "Douglas Otis" <[email-masked]>
Date: Mon, 6 Aug 2001 11:43:50 -0700

Julian,

The reject response requires the entire PDU header be returned.  That would
then require resources to store these headers for such a response.  If there
are resources to store this command, that then begs the question how many
must be stored even if only to reject?  Do you have any insight as how a
multi-connection task set resolve state with independent status
serialization?

Doug

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From: "Douglas Otis" <[email-masked]>
Date: Mon, 6 Aug 2001 12:20:10 -0700

As a follow on:

iSCSI .7

RE: Immediate Delivery

        "Please note that the number of commands used for immediate delivery
        is not limited and their delivery to execution is not acknowledged
        through the numbering scheme.  Immediate commands can be rejected by
        the iSCSI target due to lack of resources. An iSCSI target MUST be
        able to handle at least one immediate task management command and
one
        immediate non-task-management iSCSI request per connection at any
        time."

RE: Reject

        "It may happen that a target receives a PDU with a format error
(e.g.,
        inconsistent fields etc.) or a digest error (e.g., invalid payload
or
        header). The target returns the header (not including digest) of the
        PDU in error as the data of the response."

Unlike any other command, Immediate Delivery Commands are not regulated by
the Target.  It is clear however that even to reject these commands, there
needs to be resources.  If there is resouces, then there is not a problem,
if there is not resouces, then the logic seems broken.

Doug