Subject: RE: iscsi : default iscsi mode page settings.

From: "Sanjeev Bhagat (TRIPACE/Zoetermeer)" <[email-masked]>
Date: Thu, 20 Sep 2001 15:59:15 +0200

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:[email-masked]]
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.

---

From: Santosh Rao <[email-masked]>
Date: Thu, 20 Sep 2001 08:40:07 -0700

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