RE: iSCSI : Negotiable padding, was More issues.... Digest related.

["Rod Harrison" <rod.harrison@windriver.com>]

Julian,

	I'm confused. I've never seen the need for padding on the
wire, but somewhere along the line I've gotten the
impression that's what we had decided to do. This being the
case it seems a small step to have the sending side pad to
whatever alignment the receiver wants, especially since most
will want the currently specified value of 4 bytes.

	To answer your question, I believe the end system can
achieve whatever data alignment it requires regardless of
padding on the wire. My request was made on the basis that
if we were going to pad to 4 bytes on the wire anyway we
might as well go the small extra distance and make that
padding negotiable. We can set a default of 4 to be used if
padding is not negotiated.

	So, straighten me out. Are we padding on the wire or not?
And if not, why are we mentioning padding at all? Also, do
we expect to see any data padding if there are no data
digests in use?

	Thanks,

	- Rod

-----Original Message-----
From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On
Behalf Of
julian_satran@il.ibm.com
Sent: Saturday, April 21, 2001 10:31 AM
To: ips@ece.cmu.edu
Subject: Re: iSCSI : Negotiable padding, was More issues....
Digest
related.




Rod,

On the wire padding is not required at all and many of us
have resisted
padding up to the advent of markers.

Please do explain what will a padding option do that you
can't do by
yourself in the endsystem with buffer alignment - or how can
padding on the
wire stop you from getting buffer alignment all bad.

Julo

"Rod Harrison" <rod.harrison@windriver.com> on 20/04/2001
20:30:14

Please respond to "Rod Harrison"
<rod.harrison@windriver.com>

To:   ips@ece.cmu.edu
cc:
Subject:  iSCSI : Negotiable padding, was More issues....
Digest related.




Julian,

     I have a request with respect to data padding. Can we
make
the pad size login negotiable please? Preferably on a per
direction basis. This would allow the pad to be optimized
for a receivers specific requirements, e.g. cache line
alignment. Restricting padding to powers of 2 by specifying
the size as a power of 2 seems reasonable.

     For example:

     IPadSize=<any-power-of-two>
     TPadSize=<any-power-of-two>

     IPadSize=0
     TPadSize=2

     Would result in the initiator padding data to 4 byte
boundaries for the target, and the target inserting no pad
for the initiator.

     Also, a related question, if the pad is to remain
mandatory
is it expected data will be padded if no data digests are in
use?

     - Rod

-----Original Message-----
From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On
Behalf Of
julian_satran@il.ibm.com
Sent: Friday, April 20, 2001 1:45 AM
To: ips@ece.cmu.edu
Subject: Re: iSCSI : More issues.... Digest related.




1.The padding is to the next 4 byte word boundary .
2. There is a Security - Appendix

and there is a numbering /formating error in the appendix

Julo

Santosh Rao <santoshr@cup.hp.com> on 20/04/2001 03:25:49

Please respond to Santosh Rao <santoshr@cup.hp.com>

To:   IPS Reflector <ips@ece.cmu.edu>
cc:
Subject:  iSCSI : More issues.... Digest related.




Julian & All,

2 more issues :

1) If the DataSegmentLength in the BHS excludes padding
bytes, how does
the initiator determine the location of the data digest
[which is placed
after the padded data] ?
There is no knowledge of what amount of padding is in use,
since padding
can be 4 bytes or a multiple of that quantity.


2) While on the subject of digests.....are'nt there supposed
to be
login keys to indicate the use or non-use of header and data
digests ? I
can't seem to find any such login keys in the latest revs
5.91....5.92....6.000...(?)

(Section 2.2.1 states :
"The digest types are negotiated during the login phase. ").

- Santosh
 - santoshr.vcf