Re: iscsi : default iscsi mode page settings.

[Santosh Rao <santoshr@cup.hp.com>]

Sanjeev,

As my original mail indicates, you may want to refer Section 3 of iscsi Rev
7.94 (found at :
http://www.haifa.il.ibm.com/satran/ips).

[Well, now, there's a Rev 7.95 (daily rev updates.)...]

This section explains iscsi specific mode pages and calls out the default
values listed below.

- Santosh

"Sanjeev Bhagat (TRIPACE/Zoetermeer)" wrote:

> 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.
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