RE: iscsi : default iscsi mode page settings.

[Robert Snively <rsnively@Brocade.COM>]

It is true that default mode settings for Mode Pages 
are usually arranged between buyer and vendor for
maximum convenience in the buyer's systems.  It is
generally true that any setting of a Mode Page will
allow the protocol to operate correctly, except a few,
notably the first burst size parameter if 
ImmediateData is set to yes.

On the other hand, some of the iSCSI text keyed
parameters MUST be known before the protocol will
operate correctly.  ImmediateData is certainly
one of those.  As a result, you have two choices:

   a)	Make the negotiation of all such parameters
	MANDATORY during the login and after any
	reset that may change them,  or;

   b)	Define a default state that will be guaranteed
	unless and until the parameter has been explicitly
	changed.

Your choice.

Bob

> -----Original Message-----
> From: Sanjeev Bhagat (TRIPACE/Zoetermeer) [mailto:sbhagat@tripace.com]
> Sent: Thursday, September 20, 2001 6:59 AM
> To: 'Santosh Rao'; IPS Reflector
> Subject: RE: iscsi : default iscsi mode page settings.
> 
> 
> Santosh,
> 
> Where did you find these SCSI Mode page settings? At least I 
> could not find
> it in SAM-2 document? The mode select command is available in 
> SPI documents
> but they are meant for particular SCSI device and not for 
> iSCSI device? 
> 
> Be it whatever the case I would like to ask why the default value of
> MaximumBurstSize is 512 units and why is the default value of 
> FirstBurstSize
> 128 units. remember each unit is 512 bytes as defined in iSCSI 7.9x
> revisions so setting the default value of FirstBurstSize to 
> 128 units means
> 65536 bytes or 64K Bytes and similarly the value of 
> Maximumburstsize is 256K
> Bytes. Is it Ok to have the FirstBurstsize of 64KB??
> 
> Sanjeev
> 
> -----Original Message-----
> From: Santosh Rao [mailto:santoshr@cup.hp.com]
> Sent: Thursday, September 20, 2001 2:04 AM
> To: IPS Reflector
> Subject: iscsi : default iscsi mode page settings.
> 
> 
> All,
> 
> Speaking on the subject of default settings, some questions on recent
> changes to the iscsi mode select pages......
> 
> 1) Section 3 of rev 7.94 of the iscsi draft attempts to call 
> out default
> values for the iscsi  mode pages. Per my understanding, there are no
> defaults for SCSI mode pages, and all the setting are assumed to be
> disabled, unless explicitly turned on/enabled through a mode select.
> 
> IOW, the keys in scsi mode pages are defined to be enabling certain
> features and the default settings are that these features are 
> turned off
> unless a mode select is explicitly used to enable them.
> 
> However, the iscsi mode pages seems to be using the opposite 
> policy and
> is advertising default settings for mode pages, that too, 
> agreesive ones
> at that! IOW, an initiator implemenation has to explicitly 
> issue a mode
> select to disable/turn_off features rather than issue a mode select to
> turn them on.
> 
> Here's a few examples :
> 
>    * default MaximumBurstSize : 512 units
>    * default EMDP : 1 (i.e. modify data pointers is enabled by default
> !)
>    * default FirstBurstSize : 128 units. (i.e. initiators MUST use
> solicited
>      data, unless they explicitly turn it off using mode 
> select, since,
> not
>      sending solicited data when it has been negotiated 
> implies a target
> may
>      abort the I/O.
> 
> I suggest that in keeping with the scsi mode pages, NO 
> default settings
> be advertised for any iscsi mode
> pages. i.e. all defaults are conservative (set to 0), unless 
> explicitly
> turned on thru a mode select.
> 
> Comments ?
> 
> Regards,
> Santosh
> 
> "Mallikarjun C." wrote:
> 
> > Matthew,
> >
> > I completely agree that the default should be "no"!  I pointed this
> > out sometime ago myself.  Apart from what you point out, the default
> > setting for "ImmediateData" seems to be at variance with the
> > conservative default for "InitialR2T" ("yes").
> >
> > Julian, could you please consider this request?
> >
> > Regards.
> > --
> > Mallikarjun
> 
> > "BURBRIDGE,MATTHEW (HP-UnitedKingdom,ex2)" wrote:
> > >
> > > Julian,
> > >
> > > Appendix D24 (ImmediateData) does not describe the result of
> negotiation if
> > > the two sides differ. I presume that since the default is "yes",
> then only
> > > if both sides agree to "no" is immediate data turned off.  Please
> can this
> > > be stated.
> > >
> > > Additionally, I feel that the default value for 
> ImmediateData should
> be
> > > "no".
> > >
> > > Similarly, there is no statement on MaxOutstandingR2T.  Presumable
> the
> > > minimum is selected.
> 
>