RE: Data in SCSI Response or SCSI Data

["Douglas Otis" <dotis@sanlight.net>]

Julo,

Is it compliant to assume knowledge of the TCP frame by the iSCSI
application?  In many places within iSCSI discussions, references are made
of packets, frames, and datagrams as an element within iSCSI.  If creating
frame alignment is your intent, rather than corrupting TCP APIs, perhaps you
should consider SCTP.  Otherwise, such discussions are little more than a
wink and a nod at creating a frame aligned TCP.  How do you advise a change
to the TCP API to resolve frame alignment as you have just suggested?

Doug

> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> julian_satran@il.ibm.com
> Sent: Saturday, August 26, 2000 2:28 AM
> To: ips@ece.cmu.edu
> Subject: Re: Data in SCSI Response or SCSI Data
>
>
>
>
> Steph,
>
> I assume that your hardware knows when it is going to send the last SCSI
> datagram.
> In this case it can insert the status in the datagram header (not at the
> end) -
> (and BTW that is how the current draft assumes that things will be done).
>
> If you have to send sense-data (bad status) then you will send a separate
> datagram.
>
> Julo
>
> Stephen Bailey <steph@cs.uchicago.edu> on 25/08/2000 22:12:09
>
> Please respond to Stephen Bailey <steph@cs.uchicago.edu>
>
> To:   ips@ece.cmu.edu
> cc:    (bcc: Julian Satran/Haifa/IBM)
> Subject:  Re: Data in SCSI Response or SCSI Data
>
>
>
>
> > Is there anything preventing your hypothetical hardware implementor
> > to send always good status within the last block of data?
>
> It depends upon the RDMA mechanism you are using.  I admit that I have
> not studied them in detail, other than ST of course, which is
> essentially an transport protocol based upon a particular RDMA
> mechanism.  I will try to do so soon to determine if I'm all wet.
>
> However, assuming that the RDMA mechanism operates on a per-datagram
> basis, I can only imagine that you will not be able to append
> `general delivery' data to the end of an RDMA datagram.  In this case,
> you will need a separate datagram to ensure that status is delivered
> through a separate path from the data.
>
> So, while I think concatenating status and data in its general form is
> not a good idea, a good-status fast path (like the success bit) is
> definitely the right way to think about it.  Nonsuccess SCSI status is
> so rare that any compromise you can make in the nonsuccess path to
> make the success path go faster is worth it.
>
> Steph
>
>
>