RE: iSCSI Target Reset

[Charles Monia <cmonia@NishanSystems.com>]

Hi:

Sorry to reopen old issues, but unfortunately that seems necessary since
something has been lost in translation.

My concerns about TARGET RESET center on three areas:

1.  Adverse side effects at the transport layer that could affect other
users.
2.  Similar adverse side effects on the affected devices,
3.  The impact on legacy software.

The gist of my opinion on the first issue, (as expressed on the T10
reflector) is as follows:

"> > > > The ... issue is whether mechanisms, such as terget reset, 
> > > > are appropriate for a given transport.  In my view, the only 
> > > > immutable requirement is to preserve the transport-independant 
> > > > part of the semantics.  The definition of transport-specific
> > > > side effects is best handled in the appropriate transport
> > > > specification."

The point of the above is that, in my view, a protocol specification has
leeway to define the protocol-specific side effects in a rational and benign
manner provided that the observable effects on the attached devices are
preserved.

Regarding adverse device-level side effects, I also stated that:

"....restricting the operation [target reset] means providing hooks so that
only a
trusted class of initiators can perform the function.  It's a bit like
controlling access to a file so that lots of users can read it but only a
trusted few can perform a write or delete operation." 

Finally, with regard to legacy implementations, my main intent was to avoid
the situation where an operation that was previously legal becomes illegal.
In that regard, I also recall suggesting that the function be treated as a
LUN RESET broadcast to all the logical units to which the initator had
access privileges.  That would also support the notion of preventing adverse
effects on other users as well. 

At any rate, since there is a proposal to make LUN RESET mandatory (see
below), I believed this was a reasonable and consistent alternative. I
therefore felt (and continue to believe) there is no justification for
making the function optional.

Anyhow, thess views did not prevail at the meeting in question. For that
reason, the so-called NOP proposal was made as a last ditch effort to
accomodate legacy implementations by preserving a measure of backwards
compatibility (albeit token compatibility). In that regard, it seemed the
lesser evil.

> > As for leaving things out of iSCSI - the default modus
> > operandi should be to put in everything that's described
> > in SAM2 unless we can convince T10 to take the feature
> > out of SAM2.  Let's not go deciding to cast things out
> > of SCSI on T10's behalf.

So, I guess that anyone wishing to support a change in the spec is, of
course, free to pursue it in that forum. 

Charles

PS: The proposal referenced above can be found at:
ftp://ftp.t10.org/t10/document.01/01-015r2.pdf

> -----Original Message-----
> From: Elliott, Robert [mailto:Robert.Elliott@COMPAQ.com]
> Sent: Monday, April 23, 2001 5:20 PM
> To: ips@ece.cmu.edu; 'Black_David@emc.com'; 'cmonia@nishansystems.com'
> Subject: RE: iSCSI Target Reset
> 
> 
> It's not a very good situation when each device chooses the
> interpretation of TARGET RESET that it thinks is appropriate.  
> IBM's Shark might choose a different hack than Compaq's
> RA8000.  How is software supposed to make sense of this?
> 
> The rule in SAM-2 is that TARGET RESET resets every logical
> unit (subject to access controls, if implemented).  The fact
> is that in Fibre Channel, not many multi-LUN multi-port
> targets followed that rule.  The result is that software 
> cannot tell what's going to happen and may have to handle
> targets from each vendor differently.  This is not very 
> interoperable.
> 
> Charles suggested in the T10 meeting that we allow it to 
> be implemented as a no-op rather than let protocols drop 
> support for it.  That doesn't help software like Windows that 
> does expect certain effects - a no-op implementation 
> would break clustering.  By removing it from the protocol, 
> software is forced to find a suitable replacement (e.g. use 
> LOGICAL UNIT RESET or switch to persistent reservations).
> In Windows, this can be done at the port driver level
> (STORPORT improving on SCSIPORT) or at the miniport level
> (convert each target reset request into multiple LOGICAL UNIT
> RESETs).
> 
> Note that other protocols like NFS and HTTP over IP don't
> seem to have "server resets."
> 
> The recent SAM-2 change was expressly designed to encourage 
> iSCSI and SRP to drop support for TARGET RESET.  Please don't 
> keep it because you think T10 would be offended :-)
> 
> ---
> Rob Elliott, Compaq Server Storage
> Robert.Elliott@compaq.com
> 
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: Black_David@emc.com [mailto:Black_David@emc.com]
> > Sent: Monday, April 23, 2001 6:31 PM
> > To: cmonia@NishanSystems.com; ips@ece.cmu.edu
> > Subject: RE: iSCSI Target Reset
> > 
> > 
> > I agree with Charles that this is an implementation
> > issue.  If a Shark wants to reset all 32 adapters
> > when it receives a Target Reset on one of them, that's
> > a Shark implementation decision.  It's completely valid
> > to reset only the adapter that the Target Reset is
> > received on (common Fibre Channel behavior) or
> > only the iSCSI target to which the Target Reset is
> > addressed if there's more than one Target behind  
> > the adapter.
> > 
> > As for leaving things out of iSCSI - the default modus
> > operandi should be to put in everything that's described
> > in SAM2 unless we can convince T10 to take the feature
> > out of SAM2.  Let's not go deciding to cast things out
> > of SCSI on T10's behalf.
> > 
> > Thanks,
> > --David
> > 
> > > -----Original Message-----
> > > From:	Charles Monia [SMTP:cmonia@nishansystems.com]
> > > Sent:	Monday, April 23, 2001 7:12 PM
> > > To:	ips@ece.cmu.edu
> > > Subject:	RE: iSCSI Target Reset
> > > 
> > > Hi:
> > > 
> > > These seem to be implementation decisions. I don't see how 
> > that justifies
> > > removing support from the protocol.
> > > 
> > > Charles
> > > 
> > > > -----Original Message-----
> > > > From: John Hufferd [mailto:hufferd@us.ibm.com]
> > > > Sent: Monday, April 23, 2001 2:34 PM
> > > > To: Santosh Rao
> > > > Cc: ips@ece.cmu.edu
> > > > Subject: Re: iSCSI Target Reset
> > > > 
> > > > 
> > > > 
> > > > Absolutely not,  Why would we think that impacting 32 
> > different other
> > > > initiators is an OK thing to do.  By the way there are lots 
> > > > more Initiators
> > > > possible with FC on Shark, and would hope that there would be 
> > > > even more
> > > > with iSCSI.
> > > > 
> > > > I have been told that these large Storage Controllers do not 
> > > > support Target
> > > > Reset today.  So I see no loss in not supporting such an 
> > item in iSCSI
> > > > especially since many Initiators will be beyond even the 
> > distances and
> > > > mischief that is possible with FC.
> > > > 
> > > > .
> > > > .
> > > > .
> > > > John L. Hufferd
> > > > Senior Technical Staff Member (STSM)
> > > > IBM/SSG San Jose Ca
> > > > (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
> > > > Internet address: hufferd@us.ibm.com
> > > > 
> > > > 
> > > > Santosh Rao <santoshr@cup.hp.com>@ece.cmu.edu on 04/23/2001 
> > > > 01:24:02 PM
> > > > 
> > > > Sent by:  owner-ips@ece.cmu.edu
> > > > 
> > > > 
> > > > To:   ips@ece.cmu.edu
> > > > cc:
> > > > Subject:  Re: iSCSI Target Reset
> > > > 
> > > > 
> > > > 
> > > > "Dillard, David" wrote:
> > > > >
> > > > > When will STORPORT be generally available?  The latest 
> > > > STORPORT document
> > > > > that I found on the MS web site is version 0.6a, dated 
> > > > March 18, 2001.
> > > > > Given this it seems like STORPORT might not be available 
> > > > soon.  In that
> > > > case
> > > > > do you know what happens with the current drivers?  Are we 
> > > > going to be
> > > > > telling customers that if they want to use iSCSI and NT 
> > > > clustering they
> > > > have
> > > > > to update to Whistler?
> > > > 
> > > > 
> > > > [One would hope that this list does not turn into a Microsoft
> > > > release/product discussion mailing list (?) ]
> > > > 
> > > > Without going into specifics of A certain O.S., does it 
> suffice to
> > > > require that iSCSI not break existing legacy SCSI applications ?
> > > > 
> > > > If the above is a valid requirement, then, knowing that legacy
> > > > applications continue to use SCSI-2 Reserve/Release and the 
> > > > target reset
> > > > as a mechanism of breaking SCSI-2 reservations, should'nt 
> > > > iSCSI continue
> > > > to support the target reset ?
> > > > 
> > > > - Santosh
> > > > 
> > > > 
> > > > 
> > > > 
> > 
>