Re: iscsi : default iscsi mode page settings.

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

"Elliott, Robert" wrote:

> If there were not already a FirstBurstSize for other protocols
> controlled by the mode page, I'd agree - these protocol-specific
> fields shouldn't be controlled by mode pages, which can be
> changed by applications at any time.  They ought to be properties
> of the login session and controlled only by the iSCSI drivers.
>
> However, it has been defined this way for other protocols, so
> I think a compatible control is needed for iSCSI.  This makes
> protocol bridges simpler, and will avoid confusing software that
> does try to use these mode pages.  A page that appears when
> a FC target is connected to a host via FC should also appear
> with the same meaning when presented through an iSCSI bridge
> via Ethernet.

Rob,

Is the un-solicited data support offered by an iSCSI bridge tied to its
back end target's ability to support the same ?

My understanding is that the immediate data and un-solicited data
buffering limits are a measure of the iscsi bridge's buffering
capabilities and settings like FirstBurstSize and DataPDULength are
properties of the iscsi bridge rather than its back end targets. Why,
then, would it be interested in forwarding the mode sense/select to the
back-end device ? Rather, it would be attempting to filter out such
commands from the command stream destined to the back-end target and
process such commands within the bridge.

(Example : Is an iscsi bridge that is supporting back-end pSCSI devices
and older gen FCP devices that do not support FirstBurstSize prevented
from the use of un-solicited data. ? )

IMO, using the mode select/sense for setting these attributes, rather than
iscsi login keys implies MORE work for iscsi bridge developers since they
need to snoop and intercept these mode sense/select, rather than have them
negotiated/queried thru iscsi means such as login keys. They may also need
to take action preventing such mode select/sense CDBs from being delivered
to its back end for the same reason.

Regards,
Santosh


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