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    RE: iSCSI draft-07 Padding



    The burst of data (sequence in FCP-2, I assume a PDU in iSCSI) 
    carrying the last byte (as defined by the highest displacement of
    the SCSI data pointer) may be padded by 0,1,2,or 3 bytes to bring
    the last PDU to a 4-byte transfer boundary.  The number of bytes
    padded is included in the last transfer header, so they can be
    ignored and not passed to memory in an automated manner.
    
    Bob
    
    -----Original Message-----
    From: Eddy Quicksall [mailto:ESQuicksall@hotmail.com]
    Sent: Tuesday, July 24, 2001 10:30 AM
    To: Michael Schoberg; ips@ece.cmu.edu
    Subject: Re: iSCSI draft-07 Padding
    
    
    What does a Fibre Channel driver do when the ULP wants to receive data into
    memory which is not a multiple of 4 bytes long?
    
    Eddy
    
    ----- Original Message -----
    From: "Michael Schoberg" <michael_schoberg@cnt.com>
    To: <ips@ece.cmu.edu>
    Sent: Tuesday, July 24, 2001 11:13 AM
    Subject: RE: iSCSI draft-07 Padding
    
    
    > Yes, at the very least the spec should not allow padding on intermediate
    > ReadData/WriteData bursts.  I can't think of a reason why one would want
    to
    > use odd length intermediate bursts, so hopefully it's safe to restrict it.
    > Padding the last burst still seems reasonable for easy CRC calculation.
    >
    > Setting a fixed size is optional.  A minimum would avoid memory
    > fragmentation when working with memory descriptors.
    >
    > : -----Original Message-----
    > : From: Robert Snively [mailto:rsnively@Brocade.COM]
    > : Sent: Tuesday, July 24, 2001 8:34 AM
    > : To: ips@ece.cmu.edu
    > : Subject: RE: iSCSI draft-07 Padding
    > :
    > :
    > : Fibre Channel's approach to this problem is to prohibit padding
    > : for all transfers except the transfer that moves the last bytes
    > : in the last (or highest pointer value) burst of data.  Intermediate
    > : bursts are required to end on 4-byte boundaries, regardless of
    > : tranfer order as allowed by EMDP.
    > :
    > : Bob
    > :
    > : ----- Original Message -----
    > : From: "Michael Schoberg" <michael_schoberg@cnt.com>
    > : To: <ips@ece.cmu.edu>
    > : Sent: Friday, July 20, 2001 4:27 PM
    > : Subject: iSCSI draft-07 Padding
    > :
    > :
    > : > I couldn't find anything in the latest iSCSI spec
    > : (draft-07) that prevents
    > : > someone from issuing multiple padded PDU's for iSCSI Data
    > : In/Out segments.
    > : > I guess I'm worried that someone could issue padded
    > : odd-length write/read
    > : > data when it wasn't necessary.  Example: When moving a 512 byte disk
    > : sector
    > : > an initiator/target could legally issue 512 1-byte DataSegmentLength
    > : > messages (each padded up to a 32-bit boundary).  This isn't
    > : the sort of
    > : data
    > : > stream one would expect, but it's allowed in the draft.
    > : >
    > : > This also leads into whether fixed or minimum length data
    > : segments (for
    > : all
    > : > but the last) would be nice to include as part of the spec.
    > :  It may result
    > : > in a simpler software/hardware design.
    > : >
    > :
    >
    


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Last updated: Tue Sep 04 01:04:13 2001
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