Subject: RE: iSCSI: padding on intermediate sequences

From: Sukha Ghosh <[email-masked]>
Date: Tue, 26 Mar 2002 15:40:29 -0500

Just to clarify,

What Eddy (please correct me if I am wrong) is asking is that if a Data-in
response is multiple sequences of Data-In PDUs then the ending Data in PDUs
(F = 1)of intermediate sequences must also follow the 4-byte alignment rule
with pure data payload no padding. This means that only the last data-in PDU
can have padding, if necessary.   

-----Original Message-----
From: Robert D. Russell [mailto:[email-masked]]
Sent: Tuesday, March 26, 2002 2:48 PM
To: Eddy Quicksall
Cc: ips@ece. cmu. edu (E-mail)
Subject: Re: iSCSI: padding on intermediate sequences

Eddy:

I may not be understanding you correctly, but the
words in section 9.7.7 I believe mean that these data
segments should contain an integer number of 4 byte words
of data, not arbitrary "pad" bytes.  If the data segment
length is a multiple of 4 then there will be NO pad bytes.

There seems to be confusion over your use of "pad"
and the standard's use of "pad".  Would you please clarify?

Thanks,
Bob

On Tue, 26 Mar 2002, Eddy Quicksall wrote:

> Section 9.7.7 says:
>
> The Data Segments of Data-in and Data-out PDUs SHOULD be filled to the
> integer number of 4 byte words (real payload) unless the F bit is set
> to 1.
>
> This allows one to pad intermediate sequences of a transfer. But, there
are
> reasons why padding on intermediate sequences within a transfer can make
> life difficult.
>
> Can we forbid padding on all but the last PDU for the transfer? If that is
> objectionable, could we forbid padding on all but the last PDU of a
transfer
> if DataInOrder=yes.
> Eddy

---

From: "Anshul Chadda" <[email-masked]>
Date: Tue, 26 Mar 2002 17:25:17 -0500

suppose there is a requirement that a Data-In PDU with F-bit set (denoting
just end of sequence and not last data-in pdu for the command) have real
data (no pad bytes) in its last 4 byte word.

Now the target has to keep track of data over sequences. if a target doesn't
have enough real data to fill the last data-in pdu (in a sequence) to
integer number of 4 byte words, then it has to wait (don't know for how
long) for data that might belong to next sequence. this will increase the
work for target, won't it? and it will break the concept of sequences too as
we want the sequences to be independent of each other and not wait for each
other.

hope i got the question correct!!

Anshul

----- Original Message -----
From: "Sukha Ghosh" <[email-masked]>
To: "'Robert D. Russell'" <[email-masked]>; "Eddy Quicksall"
<[email-masked]>
Cc: "ips@ece. cmu. edu (E-mail)" <[email-masked]>
Sent: Tuesday, March 26, 2002 3:40 PM
Subject: RE: iSCSI: padding on intermediate sequences