RE: iscsi : default iscsi mode page settings - Consensus call

["Elliott, Robert" <Robert.Elliott@compaq.com>]

My concern is for bridges.

If an iSCSI initiator is talking to a FC target through an 
iSCSI to FC bridge, the target will include these mode pages.
Does the bridge need to intercept the MODE SENSE/SELECT
commands and hide the presence of these pages?  Does the
bridge have to generate its own MODE SELECT commands
on the FC side to match the iSCSI key settings?

Similarly, if a FC initiator is talking to an iSCSI target
through an FC to iSCSI bridge, and the iSCSI target does not 
have these pages, does the bridge have to create fake pages?
Without them, it doesn't look FCP-2 compliant.

I think it's better if iSCSI looks like the other SCSI
protocols and controls these features with the existing
mode pages.
---
Rob Elliott, Compaq Server Storage
Robert.Elliott@compaq.com





> -----Original Message-----
> From: Santosh Rao [mailto:santoshr@cup.hp.com]
> Sent: Thursday, September 27, 2001 11:36 AM
> To: Julian Satran
> Cc: ips@ece.cmu.edu
> Subject: Re: iscsi : default iscsi mode page settings - Consensus call
> 
> 
> Julian,
> 
> As we've discussed earlier, SCSI level software looking at transport
> specific mode pages MUST be aware of the format of those mode 
> pages for
> the given transport. (For example : The format of the
> disconnect-reconnect mode page is different for SPI-4, FCP-2, SRP &
> iSCSI).
> 
> Thus, any SCSI level software needs to first be upgraded when new SCSI
> transports come along, before it can understand the mode page 
> formats of
> that transport.
> 
> By declaring the iscsi mode page fields as reserved, you would not be
> breaking any legacy software. There is no legacy issue here. 
> 
> Regards,
> Santosh
> 
> 
> Julian Satran wrote:
> > 
> > Santosh,
> > 
> > You ignore the fact that there might be SCSI level software 
> that may want
> > those values.
> > 
> > Julo
> > 
> > 
> >                     Santosh Rao
> >                     <santoshr@cup.       To:     
> "'Black_David@emc.com'" <Black_David@emc.com>,
> >                     hp.com>               ips@ece.cmu.edu
> >                     Sent by:             cc:
> >                     owner-ips@ece.       Subject:     Re: 
> iscsi : default iscsi mode page
> >                     cmu.edu               settings - Consensus call
> > 
> > 
> >                     27-09-01 04:02
> >                     Please respond
> >                     to Santosh Rao
> > 
> > 
> > 
> > David,
> > 
> > By specifying that these values be read-only in mode pages, we have
> > retained some of the complexity that lies in having to go 
> across layers
> > to communicate the defaults to the scsi layer, or 
> alternatively to have
> > the target's iscsi layer snoop for such mode sense commands 
> and respond
> > to them.
> > 
> > I would prefer to see iscsi declare these fields as reserved in the
> > iscsi definition of the mode pages [like is done in SPI-4 for
> > FirstBurstSize] so that this issue does not arise at all.
> > 
> > Thanks,
> > Santosh
> > 
> > > > If some aspect of the
> > > > SCSI protocol requires that they be readable via a mode page,
> > > > the mode page values will be read-only.
> > 
> > #### santoshr.vcf has been removed from this note on 
> September 27 2001 by
> > Julian Satran
> 
> -- 
> ##################################
> Santosh Rao
> Software Design Engineer,
> HP-UX iSCSI Driver Team,
> Hewlett Packard, Cupertino.
> email : santoshr@cup.hp.com
> Phone : 408-447-3751
> ##################################
>