Re: iSCSI : login keys & mode page settings

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

Stephen Bailey wrote:
> 
> > +++ It is all about function - several people felt that the (primitive)
> > negotiation element in the text commands is better than trying to set a
> > parameter to an unacceptable value and finding this out through a mode
> > sense
> > ++++
> 
> Several other people seem to have felt that it was better not to have
> redundant mechanisms for manipulating this sort of parameter.  How do
> you decide?
> 
> Steph


Julian,

I would prefer a single mechanism as opposed to multiple redundant
mechanisms to set negotiation elements. (Reduce/eliminate options.). In
addition, I have the following concerns [some of which I have raised
repeatedly and have NOT gotten a reply. I would appreciate if you could
kindly comment on ALL of these.] :

1) The draft makes repeated references to a "iSCSI LUN Control Mode
Page". There is NO such page per SPC-2. The references must be changed
to "iSCSI protocol specific LUN page".

2) The new daily release of the draft (5.92 when I last checked) has now
introduced EnableACA as a negotiable login key. All references to
EnableACA are redundant and should be removed for the following reasons
:

a) An initiator knows whether a target supports ACA from the NACA bit in
the INQUIRY response. When a target indicates support for ACA, the
initiator can use it by setting the NACA bit in the CDBs it sends. There
is NO need for any sort of negotiation of this behaviour above and
beyond what is already provided thru SCSI mechanisms.

b) The ACA is a SCSI ULP concept and iSCSI should not be negotiating its
use or lack thereof. This is done thru the NACA bit in CDBs.

c) (As a side note, the description of EnableACA on pg 127 refers to its
presence in the lun control mode page, but it is actually present in the
protocol specific port page.)

d) ACA is a LUN-level (more an I/O level) control option. It MUST NOT be
negotiated on a per-session basis. SCSI allows initiators to request ACA
behaviour on a per I/O basis through the use of NACA bit in the CDBs.


2) 
> On a side note, the EnableCmdRN  & CmdRN fields should be re-named to
> EnableCRN and CRN to reflect the same semantics and context as the CRN
> defined in SAM-2 and FCP-2.
>
> +++ what's in a name... +++

Consistency for one ! (Any strong reasons not to call this CRN, as SAM
and FCP do ?)


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. 


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 ?


5)
> If these operational parameters are allowed to be set thru 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 ?
>

6) 
> Should saved page settings be allowed thru iSCSI ?

I did not see any comments on the above issues (?).

- Santosh
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