RE: iscsi : iscsi parameter default values

["Somesh Gupta" <somesh_gupta@silverbacksystems.com>]

John makes a good point about the power of immediate
data, and it being a significant differentiator and
advantage over FC for short reads/writes.

This is one aspect of the protocol I think most people
would agree is beneficial. The disagreement is more
along the lines of whether Target should be made to
change their current APIs.

There are other defaults (such as number of connections
per session) on which we probably have much bigger
disagreements about how useful the base feature is.

My question is about how we want to set the defaults.
Should we be conservative as Santosh suggests, or
base it on desired behavior (as John suggests).

Once we decide that, we could talk about the other
defaults.

Somesh
> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> John Hufferd
> Sent: Friday, September 28, 2001 11:09 AM
> To: Robert Snively
> Cc: ips@ece.cmu.edu
> Subject: RE: iscsi : iscsi parameter default values
>
>
>
> Robert,
> We have had this debate before, and I guess the sides are still polarized.
> However, a number of folks believe that immediate is easier to handle then
> R2T (since all the information they need is with the PDU), and the
> conservative option.  The main discussion has been since they also want to
> have  R2T they did not want to have two code paths. However, when folks
> have looked at the effort to support immediate data, they have found it to
> be trivial.
>
> The payback of NOT having multiple round trips to get the data is an
> important feature, and when you think about all the error
> recovery items we
> have been discussing, it is clear that immediate data makes every thing
> easier.
>
> The important performance improvements are so important to iSCSI (in my
> mind) that if the worse the Target has to do if it can not handle
> immediate
> data, is to send the Text Key of "ImmediateData=no", I do not
> think this is
> a problem.  We need to have this performance feature thought about as a
> normal property of iSCSI, so that every one that talks about the
> advantages
> of iSCSI can include this, with out a bunch of qualifying statements.
> Having this as the default is one way to keep this thought at the front of
> everyone's mind.
>
> .
> .
> .
> John L. Hufferd
> Senior Technical Staff Member (STSM)
> IBM/SSG San Jose Ca
> Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
> Home Office (408) 997-6136
> Internet address: hufferd@us.ibm.com
>
>
> Robert Snively <rsnively@brocade.com> on 09/28/2001 08:25:45 AM
>
> To:   John Hufferd/San Jose/IBM@IBMUS, Julian Satran/Haifa/IBM@IBMIL
> cc:   ips@ece.cmu.edu
> Subject:  RE: iscsi : iscsi parameter default values
>
>
>
> I vote no as the default value on ImmediateData.
>
> A default value of yes on ImmediateData requires implementation
> of the most complex and demanding mode of operation as the
> default.  SCSI has traditionally made its default behavior the
> simplest and most encompassing, setting more sophisticated
> behavior by subsequent agreement.  While it may be your earnest
> desire to encourage the implementation of this function, it
> is not appropriate to demand that as the default behavior
> of all devices.  In particular, there is no special benefit
> to providing ImmediateData in low-cost local sub-lans.
>
> If you want to encourage it in a profile, fine, but demanding
> it as the default in the core standard is not appropriate.
>
> Note that the behavior of SCSI is traditionally managed
> entirely by the target.  As such, there has never before now
> been a requirement for the target to, as a default, accept
> any PDU except a command or task management function
> that was not explicitly solicited.  That is one of the mechanisms
> that assists SCSI in achieving a low-overhead zero copy
> capability while operating with a large number of initiators
> and with deep command queues.
>
> Bob Snively                        e-mail:    rsnively@brocade.com
> Brocade Communications Systems     phone:  408 487 8135
> 1745 Technology Drive
> San Jose, CA 95110
>
>
>
> > -----Original Message-----
> > From: John Hufferd [mailto:hufferd@us.ibm.com]
> > Sent: Friday, September 28, 2001 1:33 AM
> > To: Julian Satran
> > Cc: ips@ece.cmu.edu
> > Subject: RE: iscsi : iscsi parameter default values
> >
> >
> >
> > I also agree with this.  It should be yes.
> >
> > .
> > .
> > .
> > John L. Hufferd
> > Senior Technical Staff Member (STSM)
> > IBM/SSG San Jose Ca
> > Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
> > Home Office (408) 997-6136
> > Internet address: hufferd@us.ibm.com
> >
> >
> > Julian Satran/Haifa/IBM@IBMIL@ece.cmu.edu on 09/27/2001 09:50:21 AM
> >
> > Sent by:  owner-ips@ece.cmu.edu
> >
> >
> > To:   ips@ece.cmu.edu
> > cc:
> > Subject:  RE: iscsi : iscsi parameter default values
> >
> >
> >
> >
> > The one that I have trouble living with is ImmediateData.
> > This is important
> > for low-end desktops and hardly matters for large boxes.
> > As such I would suggest it stays as yes.
> >
> > Julo
> >
> >
> >
> >                     "Eddy
> >                     Quicksall"            To:     "'Santosh Rao'"
> > <santoshr@cup.hp.com>,
> >                     <EQuicksall@med        <ips@ece.cmu.edu>
> >                     iaone.net>            cc:
> >                     Sent by:              Subject:     RE:
> > iscsi : iscsi
> > parameter default values
> >                     owner-ips@ece.c
> >                     mu.edu
> >
> >
> >                     27-09-01 17:22
> >                     Please respond
> >                     to "Eddy
> >                     Quicksall"
> >
> >
> >
> >
> >
> > I like your defaults below.
> >
> > But, section 5 says:
> >
> >  The initial Login request MUST include the InitiatorName and
> >  SessionType key=value pairs.
> >
> > Since SessionType is REQUIRED, naming a default would imply a
> > possible typo
> > in the spec.
> >
> > Eddy
> >
> > -----Original Message-----
> > From: Santosh Rao [mailto:santoshr@cup.hp.com]
> > Sent: Wednesday, September 26, 2001 10:29 PM
> > To: ips@ece.cmu.edu
> > Subject: iscsi : iscsi parameter default values
> >
> >
> > All,
> >
> > With the issue of mode page vs. login keys having [almost] drawn to a
> > close, I would like to
> > raise the below issues again, on the subject of default
> > values for login
> > keys and other iscsi
> > parameters :
> >
> >
> >    * In keeping with traditional use of scsi mode pages, iscsi should
> > not specify any default
> >      settings for any mode pages that continue to exist for iscsi.
> > "Default values" for mode
> >      pages are target specific and should not be bound to the protocol
> > draft.
> >
> >    * MORE IMPORTANTLY, I read the default for EMDP as being set to 1
> > :-<  This implies that
> >      targets must be always prepared to deal with out of
> > order data and
> > initiators must be
> >      prepared to deal with out of order data, unless the initiator
> > performs a mode select to
> >      disable it. [which defeats all the previous advantages
> > gained thru
> > mandating use of login
> >      keys for other negotiations.]. A default, if it were to exist,
> > should be 0. (in-order, by
> >      default).
> >
> >    * Conservative specification of defaults for login keys along the
> > following lines :
> >                             MaxConnections = 1
> >                             FMarker = "no"
> >                             InitialR2T = "yes"
> >                             BidiInitialR2T = "yes"
> >                             ImmediateData = "no"
> >                             DataPDULength = 16
> >                             MaxOutstandingR2T = 1
> >                             DataPDUInOrder = "yes"
> >                             ErrorRecoveryLevel = 0
> >                             SessionType = "normal"
> >
> >    * Should the iscsi protocol require a "Lun Control Mode Page"? IOW,
> > is an EnableCRN bit
> >      required at the transport layer ? If the device server capability
> > is to be negotiated , I
> >      suggest this bit be moved to a SCSI ULP Mode Page such as the
> > "Control Mode Page", through a
> >      T10 change as a part of the SCSI changes being driven by iscsi.
> >
> > Comments ?
> >
> > Thanks,
> > Santosh
> >
> >
> > Santosh Rao wrote:
> >
> > > There are the separate issues of :
> > >
> > >    * iscsi's specification of defaults for its mode pages
> > which is not
> > in line with mode page
> > >      usage. This impacts the target's ability to enforce
> > values other
> > than the protocol
> > >      specified default, if the initiator were to not use mode
> > sense/select.
> > >
> > >    * default settings for login keys.
> > >
> > >    * Is there a need for the "LUN Control Mode Page" and whether
> > "Enable CRN" should be in a
> > >      transport specific mode page ?
> > >
> > > which need to be driven to closure as well.
> > >
> > > Regards,
> > > Santosh
> >
> >
> >
> >
> >
> >
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> >
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