Re: iSCSI: unsolicited Vs immediate; restart delay (fwd)

[julian_satran@il.ibm.com]

Mallikarjun,

Sorry - I did not see it.

Comments in text.

Julo



"Mallikarjun C." <cbm@rose.hp.com> on 08/03/2001 20:26:21

Please respond to cbm@rose.hp.com

To:   Julian Satran/Haifa/IBM@IBMIL
cc:
Subject:  iSCSI: unsolicited Vs immediate; restart delay (fwd)




Julian,

Did you by any chance respond to this, and I did not get it (I had
noticed instances of this)?

Or, do I take it that you're going to define a mechanism for the
missing functionality in the next rev of the draft?

Regards.
--
Mallikarjun


Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions Organization
MS 5668   Hewlett-Packard, Roseville.
cbm@rose.hp.com


Forwarded message:

X-Authentication-Warning: ece.cmu.edu: majordom set sender to
owner-ips@ece.cmu.edu using -f
Message-Id: <200103062019.MAA20092@core.rose.hp.com>
Subject: iSCSI: unsolicited Vs immediate; restart delay
To: ips@ece.cmu.edu
Date: Tue, 06 Mar 2001 12:19:17 PST
Reply-To: cbm@rose.hp.com
From: "Mallikarjun C." <cbm@rose.hp.com>
X-Mailer: Elm [revision: 212.4]
Sender: owner-ips@ece.cmu.edu
Precedence: bulk
Status: RO

Julian,

>To:   ips@ece.cmu.edu
>cc:
>Subject:  Re: iSCSI: draft04 questions
>
>
>
>
>Julian,
>
>Thanks.  I am not clear on some. Comments.
>
>>2. I didn't find a way for an iSCSI target to say that it does not
support
>>any unsolicited data at all.  SPC-2 specifies that a zero FirstBurstSize
>>means unlimited.
>>
>>+++ UseR2T=yes (default) and ImmediateData=no +++
>
>I am confused.  I thought this combination disallows just the "immediate"
>data, and not the unsolicited data as a whole.  The draft hints at this
>in section 1.2.5.
>     "A target MAY separately enable immediate data without
>     enabling the more general (separate data PDUs) form of
>     unsolicited data."
>=== for this case you have UseR2T=yes and ImmediateData=yes
>If I misunderstood, could you please comment how immediate data alone is
>disabled, while allowing unsolicited data of FirstBurstSize?
>=== UseR2T=no ImmediateData=no

But that puts the target in unsolicited data mode not requiring R2Ts at
all!

Sorry if I seem too slow.  Let me try again.  There are three variables -

     1. solicited data mode after FirstBurstSize    UseR2T=yes
        unsolicited data mode only                  UseR2T=no

     2. Immediate data allowed                      ImmediateData=yes
        Immediate data disallowed                   ImmediateData=no

        3. Unsolicited burst (immediate & separate) allowed     ??
           Unsolicited burst not allowed                        ??

FirstBurstSize can be used for (3), but a zero FirstBurstSize means
"unlimited" than "not allowed".  My original question was how one can
distinguish the two.

I would be glad to be corrected, if I am misinterpreting the usage of
UseR2T.
+++ the confusion stems from the  role of UseR2T.  UseR2T is all about
allowing an unsolicited first burst.  After the first burst you need always
R2T.
You are left now with only 2 parameters controlled by the two variables.
The only think still open is that for comletness it is probably advisable
to have for Immediate also a bit in the corresponding mode page bit+++
+++++++++++++++++++++++++++++++++++++++
>Do I take it then that the draft currently doesn't specify the maximum
time
>the targets should keep the session & connection records around hoping
>for a restart?  I would strongly recommend adding that as an additional
>field in the payload, since that is a resource allocation and scalability
>issue.
>
>=== I assume that a traget can figure out by itself after a while that
>there is no rendezvous - but I am open to requests

There's no architected mechanism to figure out on its own!  Either it
has to keep the (session, connection, task) states around for a long time,
OR it can clean up the these states and trigger an unnecessary ULP
recovery on the initiator which is surprised at an unexpected restart
failure
(keep in mind that initiator may not be able to restart a login precisely
after the "minimum time" specified, typically there's an aggregation
of multiple O/S timer requests into one master handler).  Providing an
upper limit is a cleaner, safer design for both initiator and target.
+++ I will consider it for 06 - no promise though -:) the problem with
limits of this kind is who's time counts +++

Thanks.
--
Mallikarjun


Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions Organization
MS 5668   Hewlett-Packard, Roseville.
cbm@rose.hp.com