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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: reusing ISID for recovery
Thanks - I started feeling bad. I could not get a message through. Julo
"Dev" <deva@stargateip.com> on 29-08-2001 19:03:40
Please respond to <deva@stargateip.com>
To: Julian Satran/Haifa/IBM@IBMIL, <ips@ece.cmu.edu>
cc:
Subject: RE: iSCSI: reusing ISID for recovery
Julian,
>But - as this is bound to bring
>many an initiator writer to set always
>the bit to "just cover for the case" I propose that the command fails if
>the X bit was on but there was no need for it to be on.
The only need to set the X-bit (when ISID, TSID=0) could be to forcibly
close a pre-existing session, if any in the target right?
I agree with this proposal, as this forces the initiator to issue the
command
with an X-bit only when there is an error (a session already exists).
I also like that returning an error when there is no need to set an X-bit,
as it discourages the initiators to set the X-bit by default, for opening
a session.
Thanks
Deva
Platys Communications.
I think that making a new session bring down an old one makes just too easy
for common mistakes.
The scheme I've proposed - like the original option B - avoids just that by
letting the target know that this
was intentional - by adding the X bit. But - as this is bound to bring
many an initiator writer to set always
the bit to "just cover for the case" I propose that the command fails if
the X bit was on but there was no need for it to be on.
I hope that this will get us to have a scheme in which both the common
mistakes can't do harm and the initiator writers
will not get away by always having the X bit on.
The price is a login in 2 steps in case of recovery - and I think this is
acceptable.
Julo
Jim Hafner/Almaden/IBM@IBMUS@ece.cmu.edu on 28-08-2001 19:04:34
Please respond to Jim Hafner/Almaden/IBM@IBMUS
Sent by: owner-ips@ece.cmu.edu
To: ips@ece.cmu.edu
cc:
Subject: RE: iSCSI: reusing ISID for recovery
Julo,
I'm unclear why you think that option A isn't viable and why you think a
more complicated protocol is required here.
If the initiator 'lost his way' such that he thinks he has an existing
session, then he does the normal error recovery for that scenario (a la the
mechanisms Mallikarjun noted). If he 'lost his way' so badly that he
doesn't even know he has an existing session, then option A is probably the
right thing to do. In this case, he won't even know he's lost his way so
can't expect to set the X bit rationally. He'd either not set it, and then
we need a rule for what the target does then OR he sets it knee-jerk in
which case there's no point in having it (as Marj, Deva, et al, have
argued).
In short, if he has knowledge of a lost session, he does session recovery.
If not, he just logs in and the target cleans up its end.
I'd like to close this issue as well, should there be a call for consensus?
Jim Hafner
Julian Satran/Haifa/IBM@IBMIL@ece.cmu.edu on 08/27/2001 09:39:03 pm
Sent by: owner-ips@ece.cmu.edu
To: ips@ece.cmu.edu
cc:
Subject: RE: iSCSI: reusing ISID for recovery
Marjorie, Jim, Mallikarjun, Deva & all
Let's attemp to close that optimization that is so dear to your hearts.
If we go for the following scheme (very close to B):
The initiator knows "that he lost his way" (in the initiator jungle tough)
and issues a Login + ISID + TSID=0 + X bit on (meaning
" I think I have an old session - please clean it up for me" and open a new
one) then the target may do one of the following:
- before going to the effort of authenticating the new initiator check if a
session exist (if he has the initiator name) or go to authentication if it
does not
- If he has a session then clean it and create a new one
- If he does not have a session - we have 3 options:
a)- tell him hid did not have an old session and drop him
b)- tell him he did not have an old session but nevertheless create a new
one
c)- create a new session and do not tell him
With option a we are close to the old option c but the initiator does not
have to find the old session he can do now safely a new login
With b & c we are back at the old b.
Which one would you give your kingdom for ( and my peace!).
Julo
"Dev" <deva@stargateip.com>@ece.cmu.edu on 28-08-2001 01:44:15
Please respond to <deva@stargateip.com>
Sent by: owner-ips@ece.cmu.edu
To: "KRUEGER,MARJORIE \(HP-Roseville,ex1\)" <marjorie_krueger@hp.com>,
<ips@ece.cmu.edu>
cc:
Subject: RE: iSCSI: reusing ISID for recovery
All,
When a session is already running authenticated, a login request with the
same
ISID + initiator fails authentication. Will the session continue to run?
Or
if the target fails during parameter negotiation?
I guess, yes. i.e. target will not act on the existing session, until
the login completes successfully. Or are there exception to these?
Thanks
Deva
Platys Communications
> -----Original Message-----
> From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
> Sent: Saturday, August 25, 2001 12:23 AM
> To: ips@ece.cmu.edu
> Subject: RE: iSCSI: reusing ISID for recovery
>
>
>
> It may be another OS running on the same machine or CPU
> complex or it could
> be an attack.
> In any case if the initiator is up and fine he can as well do logout.
> It is a rare enough event for us not to try to optimize.
>
> The reboot is the only case in which the initiator can't
> logout and about
> which we care.
>
> And I would like to remind you all that we where on this
> exact thread more
> tan 3 months ago (other players).
> I just restated the rationale for an (apparent) newcomer.
>
> Julo
>
> "KRUEGER,MARJORIE (HP-Roseville,ex1)"
> <marjorie_krueger@hp.com>@ece.cmu.edu
> on 25-08-2001 03:51:43
>
> Please respond to "KRUEGER,MARJORIE (HP-Roseville,ex1)"
> <marjorie_krueger@hp.com>
>
> Sent by: owner-ips@ece.cmu.edu
>
>
> To: ips@ece.cmu.edu
> cc:
> Subject: RE: iSCSI: reusing ISID for recovery
>
>
>
> I don't see how Option A is prone to "wild closing of sessions". The
> target
> is only looking for sessions with this particular initiator
> and closing
> them
> if the ISID matches.
>
> If an initiator doesn't have a valid TSID (login w/TSID=0),
> it means it has
> lost state entirely (reboot) or knows it wants to immediately reset a
> session (NIC failure). How could there possibly be a case where the
> initiator has an active valid session with the same ISID, but
> just doesn't
> know about it?? Rejecting the login seems pointless, since
> obviously the
> initiator either has a bug or intends to quickly reset the session.
>
> The behavior chosen (Option C) will cause the initiator's
> recovery to be
> delayed while the target NOPs all the connections and waits
> for them to
> time
> out - this will only delay the initiators recovery
> unnecessarily. I can't
> help but think this will cause long term problems for the protocol.
>
> Marjorie Krueger
> Networked Storage Architecture
> Networked Storage Solutions Org.
> Hewlett-Packard
> tel: +1 916 785 2656
> fax: +1 916 785 0391
> email: marjorie_krueger@hp.com
>
> > -----Original Message-----
> > From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
> > Sent: Thursday, August 23, 2001 9:39 PM
> > To: ips@ece.cmu.edu
> > Subject: Re: iSCSI: reusing ISID for recovery (Was: RE: iSCSI
> > - Change -
> > Login/Text...)
> >
> >
> >
> > Mallikarjun,
> >
> > On your point 1 that is what is stated today in the draft.
> >
> > On your point 2 option C is the one we took in the draft, after some
> > debate.
> >
> > Option A is prone to "wild closing of sessions" and option B is also
> > relaying to much on the good behaviour of the
> > client. It also introduces a "feature" that complicates
> login/logout.
> >
> > Our postion on this is that the initiator should logout the session
> > explicitly if it can (and in this case it can as the target
> > has ascertained
> > that the session is alive).
> >
> > I agree that you may want to update the stayte diagram to
> > reflect this.
> >
> > Julo
> >
> >
> > "Mallikarjun C." <cbm@rose.hp.com>@ece.cmu.edu on
> 24-08-2001 01:46:40
> >
> > Please respond to cbm@rose.hp.com
> >
> > Sent by: owner-ips@ece.cmu.edu
> >
> >
> > To: ips@ece.cmu.edu
> > cc:
> > Subject: iSCSI: reusing ISID for recovery (Was: RE: iSCSI
> - Change -
> > Login/Text...)
> >
> >
> >
> > Julian and all:
> >
> > This thread mirrors another discussion some of us are
> > having in a different forum. Following (two bullets 1
> > & 2 below) is what I proposed there, attempting to address
> > two issues -
> > a) how to recover sessions when target and the initiator
> > have conflicting views of the same TCP connection(s)?
> > (Initiator NIC fails, but there's no I/O activity,
> > and the target doesn't see any connection failure.)
> > b) More specifically, how to address the above problem
> > when the initiator *does not want* to re-instate failed
> > connections since it only implements the mandatory
> > session recovery?
> >
> > This could add clarity or muddle things up here, though hopefully
> > the former...
> >
> > 1 If login is sent with the same ISID, same TSID, same CID
> and X-bit,
> > then it means a failed connection is being re-instated (whether
> > or not there are multiple connections in the session). This login
> > attempt must be done before the connection timeout
> (transition M1),
> > or if this is the only connection in the session, also before the
> > session timeout (transition N6) - to be counted as a connection
> > reinstatement effort.
> > o CmdSN counters (CmdSN, ExpCmdSN) are continued.
> > Initiator
> > must do command plugging when there's a mismatch
> > between its CmdSN and ExpCmdSN in the login response.
> > o Since this is an implicit connection logout, all
> > the active
> > tasks on the connection are either internally
> terminated,
> > or made non-allegiant (based on ErrorRecoveryLevel=x/y,
> > TBD) for recovery.
> >
> > 2 If login is sent with the same ISID and TSID=0, the session (if it
> > exists on the target) is being cleared and any active connections
> > that the target sees must be immediately (at the end of the login
> > process including any initiator authentication) transport reset.
> > Initiator may attempt this only after it ascertains a
> > session failure
> > on its end (ie. all connections entered RECOVERY_START).
> > o CmdSN counters get reset. Initiator has to perform the
> > currently defined session recovery actions.
> > o All active tasks of the session are internally
> > terminated.
> >
> >
> > Essentially, I was proposing extending the same notion of "implicit
> > logout" of a connection to the session level. The options that I
> > see are -
> >
> > A) Should iSCSI let it happen by default as stated above (ie.
> > same ISID, TSID=0 always wipes out the
> pre-existing session
> > on target, since we are mandating it to be used only when
> > initiator sees a session failure)?
> > B) Should iSCSI mandate making this intended cleanup explicit
> > by setting a bit (Say C-bit, for Clear) in the
> Login Command
> > PDU to prevent an accidental session cleanup with a buggy
> > initiator code?
> > C) Should iSCSI merely state that targets must ascertain
> > the connection state(s) whenever a new session creation
> > attempt is made with a known ISID and TSID=0? (sort of
> > defeats the intention of the initiator wanting quicker
> > session recovery since the Login command PDU would have
> > to idle till target ascertains the connection state(s)).
> >
> > I prefer A, or B.
> >
> > Going with A or B means that the description of transition N3
> > in the session state diagram would have to change to:
> > Last LOGGED_IN connection had ceased to be LOGGED_IN,
> > or a Login Command requesting clearing the session (also
> > with C-bit set, if option B) was received by the target.
> >
> > The transition N7's description would have to be augmented as
> > well to:
> > Session recovery attempt with an implicit logout,
> > or connection reinstatement/new CID addition.
> >
> > Comments?
> > --
> > Mallikarjun
> >
> >
> > Mallikarjun Chadalapaka
> > Networked Storage Architecture
> > Network Storage Solutions Organization
> > MS 5668 Hewlett-Packard, Roseville.
> > cbm@rose.hp.com
> >
> >
> > >Stephen,
> > >
> > >That can happen as the target may set-up completely new TCP
> > connections
> > >(the old sockets are still there and look OK).
> > >Untill the login is progessing he assumes that this is
> just another
> > >open-session attempt. Then he checks the old session and the
> > session is
> > >dead (initiator has closed the connections).
> > >
> > >The target has to distinguish only between a session that is
> > alive (and
> > >reject the new one) and one that its dead in which case it
> > can clean-up.
> > >
> > >Julo
> > >
> > >"Wheat, Stephen R" <stephen.r.wheat@intel.com> on
> 23-08-2001 22:50:56
> > >
> > >Please respond to "Wheat, Stephen R" <stephen.r.wheat@intel.com>
> > >
> > >To: Julian Satran/Haifa/IBM@IBMIL, ips@ece.cmu.edu
> > >cc:
> > >Subject: RE: iSCSI - Change - Login/Text commands with the
> > binary stage
> > co
> > > de
> > >
> > >
> > >
> > >Julian,
> > >
> > >I don't understand your answer. For the scenario given, I
> > would presume
> > >then that the target would reject the new session attempt,
> > as it sees the
> > >previous session still "alive". What is there to tell the
> > target that
> > this
> > >is any different from when the Initiator is erroneously using the
> > >repetitive
> > >session id?
> > >
> > >Thanks,
> > >Stephen
> > >
> > >-----Original Message-----
> > >From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
> > >Sent: Thursday, August 23, 2001 11:15 AM
> > >To: ips@ece.cmu.edu
> > >Subject: Re: iSCSI - Change - Login/Text commands with the
> > binary stage
> > >co de
> > >
> > >
> > >Stephen,
> > >
> > >1.If the initiator goes away for a while and reboots and
> there was no
> > >activity on the connections
> > >the target may see a session alive (I am not sure that it
> > has to appear on
> > >the state diagram but maybe).
> > >
> > >2.Again - I am not sure that the curent state diagram
> > includes death of
> > the
> > >initiator
> > >
> > >Julo
> > >
> > >"Wheat, Stephen R" <stephen.r.wheat@intel.com>@ece.cmu.edu
> > on 23-08-2001
> > >19:58:34
> > >
> > >Please respond to "Wheat, Stephen R" <stephen.r.wheat@intel.com>
> > >
> > >Sent by: owner-ips@ece.cmu.edu
> > >
> > >
> > >To: ips@ece.cmu.edu
> > >cc:
> > >Subject: Re: iSCSI - Change - Login/Text commands with the
> > binary stage
> > co
> > > de
> > >
> > >
> > >
> > >Julian,
> > >
> > >1.3.6 ISID states that the target should check to see if the
> > old session
> > is
> > >still active when a duplicate session is detected.
> > >
> > >I have two questions, the second only if you answer in the
> > affirmative on
> > >the first ;^)
> > >
> > >1. Is there a properly executed sequence of events (i.e., no
> > coding error
> > >on
> > >the target side) where the session is not active, but the
> > target hadn't
> > >taken notice of it? It appears this as a protocol-specified
> > means to work
> > >around a flaw in a target's implementation. I interpret the
> > state diagram
> > >transitions as being atomic wrt other commands. I.e., the
> > last logout
> > >would
> > >result in the various transitions of the connection/session
> > prior to the
> > >initiator starting the session up again. And the target would have
> > >completed the transitions prior to handling a new session request.
> > >
> > >2. If you answered (1) in the affirmative, then the word
> > "Active" is not
> > >consistent with the 6.3 Session State Diagram. Does this
> > mean the target
> > >got lost, due to transport failures of any sort, in its
> > transition from
> > >Q3-to-Q2-to-Q1? It sounds like the intent is to close the
> > old session if
> > >the session was in Q2 or Q4, presuming if it were in Q1, it
> > would not
> > have
> > >been found as a duplicate.
> > >
> > >Stephen
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
> >
>
>
>
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