Subject: iSCSI: Connection termination conditions

From: "Nandakumar Ramamurthy" <[email-masked]>
Date: Fri, 11 Jan 2002 15:31:21 +0530

Hi All,

Section 2.2.6 specifies two conditions for connection termination :

"Graceful connection shutdowns MUST only occur when there are no
 outstanding tasks that have allegiance to the connection and when the
connection is not in full-feature phase."

The above statement is ambiguous as to what a graceful connection
shutdown is and the conditions in which this may occur. Can "graceful
connection shutdown" be elaborated upon?

My interpretation is that there could be 2 possible cases when graceful
connection termination may occur. They are as follows:

1) A connection logout with no outstanding allegiant tasks is the first
condition.
In this case, the state of the connection is full feature.

2) The second case is when the connection is shutdown and the connection
state is not in full feature phase i.e., in SecurityNegotiation or
LoginOperationalNegotiation
phase.

Is that the correct interpretation?

Thanks,
Nandakumar
Member Technical Staff
HCL Technologies, Chennai, INDIA.
http://san.hcltech.com

---

From: "Mallikarjun C." <[email-masked]>
Date: Mon, 14 Jan 2002 10:14:56 -0800

Nandakumar,

As the preceding sentence indicates, the "graceful connection 
shutdown" being referred to is the TCP connection termination.

All the text is saying is that the an intentional and graceful 
transport connection termination must also be "graceful" wrt iSCSI.  
The first sentence in this section requires rewording for rev10, 
and I suggest ignoring it for now.

Thanks.
-- 
Mallikarjun 

Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions Organization
MS 5668	Hewlett-Packard, Roseville.
[email-masked]

---

From: "Nandakumar Ramamurthy" <[email-masked]>
Date: Tue, 15 Jan 2002 19:08:54 +0530

Hi Mallikarjun,

Agreed that there exists a distinction between a TCP connection
and an iSCSI connection.  IMHO, an iSCSI logout should precede sending
TCP FINs.  Section 2.2.6 must offer a clearer explanation in this regard.

As the section is entitled "iSCSI Connection Termination", there should be
more
focus on termination of an iSCSI connection. A separate section
entitled "TCP Connection Termination" could probably speak about TCP related
intricacies.

My understanding of iSCSI connection termination is :

An intentional and graceful iSCSI connection termination MUST occur
only through the iSCSI logout process ( either implicit or explicit ).
This is not clear from section 2.2.6.
( Are the 2 situations specified in my earlier mail valid? )

Section 3.13.5 states :
"If the Status Class is not 0, the initiator and target MUST close the TCP
connection."
Does this constitute a graceful TCP connection termination?

What are the other interpretations for a "graceful" iSCSI connection
termination?

Can "graceful" connection termination happen when it is not in full-feature
phase?  How?
Please describe the related mechanism.

Thanks,
Nandakumar
Member Technical Staff

---

From: "Mallikarjun C." <[email-masked]>
Date: Tue, 15 Jan 2002 09:59:57 -0800

Nandakumar,

There appears to be some confusion about what is implied by graceful 
connection termination.  Transport protocol (TCP for now) defines what 
a graceful transport connection shutdown is. In section 2.2.5,  iSCSI is 
only attempting to spell out *when* it should be used, so that the iSCSI 
activity also comes to a stop gracefully.

>an iSCSI logout should precede sending
> TCP FINs

*If* the connection is logged in - yes.  As far as I can tell, 2.2.6 says 
it clearly.  The case in 3.13.5 you refer is when the connection is not
yet logged in!   Keep in mind that an iSCSI connection is nothing but 
a transport connection used to carry out iSCSI activity - as defined by 
section 7.  Based on the state of the "iSCSI activity", a Logout may or 
may not always be required.

The state transitions chapter could be of some help in understanding 
how transport and iSCSI activities are intertwined during the life of an
iSCSI connection.

Hope that clears it up.
--
Mallikarjun

Mallikarjun Chadalapaka
Hewlett-Packard MS 5668 
Roseville CA 95747