Re: iSCSI : login keys & mode page settings

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

julian_satran@il.ibm.com wrote:

> 3) However, having allowed 2 mechanisms to set negotiation elements,
> iSCSI MUST
> then comment on the need to synchronize their settings in the 2 layers
> and also comment on the need to trigger a UNIT ATTENTION when changed
> through the login key mechanism.
> Again, I would vote for only 1 mechanism for setting these control
> options, rather than have to define communication schemes b/n the ULP
> and LLP to keep their values in synch and generate UNIT ATTENTION.
> 
> +++ Parameter changes originate from SCSI and iSCSI only enables another
> mechanism to convey them.
> This is an implementation issue +++

Julian,

From reading the spec, it is difficult to arrive at the above conclusion
that there currently exists only 1 layer allowed to make the changes,
albeit through 2 different mechanisms. If the changes are intended to
always originate from the SCSI layer (and I'm not sure why this should
be the case), then, would it not be more apt for the SCSI ULP to use a
mode select which is the mechanism available at this layer, rather,
than, invent down calls into the iSCSI layer to map to an equivalent
login/text key setting.

Again, I would like to request that the setting of these control options
be made from 1 layer only. 


> 4)
> > If such a level of dual control is provided, the iSCSI login
> > keys listed above be made LO (leading only) to allow for changes to
> > operational parameters only during session login. This is to
> > minimize/eliminate disruption of ongoing I/O activity that occurs due to
> > the generation of a UNIT ATTENTION CHECK CONDITION when any change is
> > made to the above paramters.
> 
> Are we in agreement on the above ?
> 
> +++ No +++

Could you please throw light on the basis for LO classification ? If
some key negotiation after a login causes disruption of all outstanding
I/O (keeping in mind its impact on tape type of devices), should'nt such
a key be not made LO (?)

IMHO, any negotiation key change that can disrupt I/O must be restricted
to login time negotiation only. (LO). This would prevent potential iSCSI
windows for disruption of tape I/O.


> 5)
> > If these operational parameters are allowed to be set through iSCSI
> > login and they also impact mode page settings, iSCSI spec should
> > describe the scope of the mode page setting in terms of whether this
> > setting is a saved page setting or not ?
> >
> +++ I don't know - I would rather think not +++
> 6)
> > Should saved page settings be allowed thru iSCSI ?
> +++ I don't know - I would rather think not +++

I agree with the above. Perhaps, the draft could explicitly state the
same. (Then again, setting these options through 1 mechanism alone would
solve this issue.)

- Santosh
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