RE: iSCSI: remove CDB from iSCSI header

["Peglar, Robert" <robert_peglar@xiotech.com>]

I agree with Mark and Matt.

As for Mark's question about padding, 2.2.3 seems to indicate so,
but padding is a good idea and the text portion of the 04/84
and 03/83 should indicate so.  Aligned CRCs are a good thing.

Rob

Rob Peglar
XIOtech Corporation
(314) 308-6983


> -----Original Message-----
> From: Mark Bakke [mailto:mbakke@cisco.com]
> Sent: Tuesday, January 23, 2001 4:51 PM
> To: Matt Wakeley
> Cc: ips@ece.cmu.edu
> Subject: Re: iSCSI: remove CDB from iSCSI header
> 
> 
> 
> I agree with Matt.  Basically, then, the iSCSI header digest 
> should cover
> everything in the first 48 bytes.  All of the messages, with 
> the exception
> of the SCSI Command Request, could easily be done this way, 
> and I think
> that we should modify that to fit Matt's idea of treating the CDB (and
> sense data) the same as SCSI data for digest purposes.  
> 
> Here's what they would all look like:
> 
> 01 - SCSI Command Request
> 
> The iSCSI header digest currently covers the 48-byte iSCSI header,
> which includes the CDB.
> 
> The data digest covers everything else, which includes extended CDB,
> bidi-read transfer length, and immediate data.
> 
> Since the command request is the only operation that really breaks
> the notion of Matt's model, I would suggest that we start the CDB
> after the 48-byte iSCSI header, and that it not be covered by the
> header digest.  We can move the bidi-read length inside the iSCSI
> header, and end up with:
> 
>   +----------------------------------------------------
>  0| Normal iSCSI header stuff for command request
>   +----------------------------------------------------
> 32| Bidi-read length
>   +--------------------------------------------------
> 36/ Reserved
>  +/
>   +---------------------------------------------------
>   | (optional header digest goes here)
>   +-------------------------------------------------
> 48| CDB
>   +--------------------------------------------------
>   | Additional CDB
>   +---------------------------------------------------
>   | Immediate Data
>   +----------------------------------------------------
>   | (optional data digest goes here)
>   +-----------------------------------------------------
> 
> The header digest would cover the first 48 bytes, and would exactly
> match the rest of the iSCSI operations.  The data digest would include
> the CDB (now contiguous with the additional CDB, as an added bonus)
> and the immediate data.  Anyone concerned with having a separate
> data integrity check for just the data when an additional CDB is
> being used should refrain from using the immediate data feature.
> 
> While we are on the topic, is anyone really planning to make 
> use of bidi-read
> and immediate data?
> 
> 
> Here is my understanding of what the digests cover with the remainder
> of the iSCSI operations:
> 
> 81 - SCSI Response
> 91 - Asynchronous Event
> 
> iSCSI header digest covers 48-byte iSCSI header
> iSCSI data digest covers the sense data, if present
> 
> 02 - Task management command
> 82 - Task management response
> 06 - Logout command
> 86 - Logout response
> 90 - R2T
> 
> iSCSI header digest covers 48-byte header
> no data, so no data digest present
> 
> 05 - SCSI Data write
> 85 - SCSI Data read
> 00 - NOP-Out
> 80 - NOP-In
> 
> iSCSI header digest covers 48-byte header
> iSCSI data digest covers the data
> 
> 04 - Text command
> 84 - Text response
> 03 - Login command
> 83 - Login response
> 
> iSCSI header digest covers 48-byte iSCSI header
> iSCSI data digest covers the text parameters
> 
> ??? Should the text be padded to a 4-byte boundary before 
> adding the data CRC?
> I think that it already says so somewhere in the spec.
> 
> --
> Mark
> 
> Matt Wakeley wrote:
> > 
> > I don't think I like this.  Header followed by digest 
> followed by more header.
> > 
> > I think this is a good opportunity to think about removing 
> the CDB from the
> > header.  This will reduce the amount of dead space used by 
> headers that do not
> > contain a CDB.  This will be beneficial when sending 
> multiple smaller PDUs (in
> > order to keep the CRC coverage high) by reducing the iSCSI 
> header overhead.
> > 
> > Change the iSCSI command so that there is an iSCSI header 
> (verified by the
> > header digest) followed by CDB "payload" (verified by the 
> data digest).  No
> > options for immediate data.  Keep it simple, like it is in 
> Fibre Channel.
> > 
> > -Matt Wakeley
> > Agilent Technologies
> > 
> > julian_satran@il.ibm.com wrote:
> > >
> > > yes,
> > >
> > > Julo
> > >
> > > "Barry Reinhold" <bbrtrebia@mediaone.net> on 22/01/2001 17:49:29
> > >
> > > Please respond to "Barry Reinhold" <bbrtrebia@mediaone.net>
> > >
> > > To:   mbakke@cisco.com, Julian Satran/Haifa/IBM@IBMIL
> > > cc:   ips@ece.cmu.edu
> > > Subject:  RE: Coverage of Data Digest when using Header Digests
> > >
> > > Ok,
> > >      So if the bidi-read length and ADDCDB fields are not 
> in the data
> > > digest
> > > then I assume we have to figure them into the header 
> digest even though
> > > they
> > > are located past the header digets. Is that the expected behavior?
> > >
> > > -----Original Message-----
> > > From: mbakke@cisco.com [mailto:mbakke@cisco.com]
> > > Sent: Monday, January 22, 2001 10:22 AM
> > > To: julian_satran@il.ibm.com
> > > Cc: ips@ece.cmu.edu; Barry Reinhold
> > > Subject: Re: Coverage of Data Digest when using Header Digests
> > >
> > > Barry-
> > >
> > > In particular, the data digest covers only the SCSI Data 
> part of an
> > > iSCSI message; the header digest covers everything else.  
> This means
> > > that in an 8k write, the data digest will cover only the 
> 8k, and the
> > > header digest will cover everything else.
> > >
> > > Hope this helps,
> > >
> > > Mark
> > >
> > > julian_satran@il.ibm.com wrote:
> > > >
> > > > Barry,
> > > >
> > > > Considering that one of the reasons to have a separate 
> header and data
> > > > digest was to enable data
> > > > to carried through proxies, virtualizers etc. the 
> current thinking is
> > > that
> > > > the data digest will cover only the data and the header 
> (including
> > > > extensions) will be covered by the header digest.
> > > >
> > > > Julo
> > > >
> > > > "Barry Reinhold" <bbrtrebia@mediaone.net> on 21/01/2001 21:50:04
> > > >
> > > > Please respond to "Barry Reinhold" <bbrtrebia@mediaone.net>
> > > >
> > > > To:   Julian Satran/Haifa/IBM@IBMIL
> > > > cc:
> > > > Subject:  Coverage of Data Digest when using Header Digests
> > > >
> > > > Julian,
> > > >      Is the Data Digest intended to cover whatever 
> follows the 48 byte
> > > > iSCSI
> > > > header? In particular in a command frame which has a 
> CDB > 16 bytes, uses
> > > > bidi, has immediate data, and is using both header and 
> data digests -
> > > what
> > > > would the data digest cover?
> > > >                                                         
>      - barry
> > > > reinhold
> > >
> > > --
> > > Mark A. Bakke
> > > Cisco Systems
> > > mbakke@cisco.com
> > > 763.398.1054
> 
> -- 
> Mark A. Bakke
> Cisco Systems
> mbakke@cisco.com
> 763.398.1054
>