Re: iSCSI: need for new data SNACK code?

["Mallikarjun C." <cbm@rose.hp.com>]

Dave,

I am glad that others are chiming in as well, :-)

>It is free to segment
> to any size <= to that and to change that size, for its own purposes, at
> any point in time w/o notifying the initiator.

That is correct for the general case, but not for the specific data SNACK
case under discussion - the spec requires the retransmitted PDUs to be 
"exact replicas" barring certain header fields, in the absence of a negotiated 
max PDU size change.
--
Mallikarjun

Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions
Hewlett-Packard MS 5668 
Roseville CA 95747
cbm@rose.hp.com

----- Original Message ----- 
From: "Dave Sheehy" <dbs@acropora.rose.agilent.com>
To: "IETF IP SAN Reflector" <ips@ece.cmu.edu>
Sent: Thursday, July 11, 2002 5:29 PM
Subject: RE: iSCSI: need for new data SNACK code?


> 
> > > If the target makes
> > > its own choice to resegment, and the initiator doesn't think the
> > > target resegmented, there are error scenarios that combine this with
> > > corrupt Data PDU headers to cause the initiator to successfully
> > > complete a SCSI command that has not delivered all its data
> > > (the resegmented PDUs caused the Data PDU count to match the ExpDataSN
> > > value in the response that should have been discarded, but wasn't).
> > > While these should be rare, their consequences can be catastrophic.
> > 
> > What do you mean by "if the target makes it's own choice to resegment"?
> > Sounds like a target bug to me.  It feels like you're making this look more
> > complicated than it really is.
> 
> The only promise the target has made to the initiator is that it will not
> send a segment larger than MaxRecvDataSegmentLength. It is free to segment
> to any size <= to that and to change that size, for its own purposes, at
> any point in time w/o notifying the initiator. I don't think the spec says
> anything about requiring the target to use a constant segment size. 
> Therefore, the described behavior is perfectly legal and not a bug as you 
> seem to believe.
> 
> Dave
> 
>