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    RE: iSCSI variable CDB length

    • To: <>
    • Subject: RE: iSCSI variable CDB length
    • From: "Elliott, Robert (Server Storage)" <>
    • Date: Mon, 10 Jun 2002 09:01:07 -0500
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    • Thread-Topic: iSCSI variable CDB length

    > -----Original Message-----
    > From: Michael J. S. Smith (PacBell) [] 
    > Sent: Sunday, June 09, 2002 2:24 PM
    > Subject: variable CDB length
    > I'm trying to bound some of the iSCSI structures. This email 
    > is regarding the AHS for extended CDBs.
    > The following (page 37 of the PDF, page 7 in the draft page 
    > numbering) is from 
    > [quote]
    > Command descriptor block (CDB): The structure used to communicate 
    > commands from an application client to a device server. A CDB may 
    > have a fixed length of up to 16 bytes or a variable length of 
    > between 12 and 260 bytes.
    > [end quote]
    > I can't find another reference within the 442 pages of the 07 
    > draft of SPC-3 to the 260-byte maximum length for a 
    > variable-length CDB.
    > 1. Is the 260-byte figure in the definitions section of the 
    > 07 draft of SPC-3 correct?
    The variable length CDB structure (spc3r07 table 7) has an 8 byte
    header, with a one byte ADDITIONAL CDB LENGTH field indicating the
    additional size in bytes.  That field must be a multiple of 4, so
    the maximum value is 252, restricting the maximum CDB length 
    to 260 bytes.
    > 2. Is it intended that the maximum length of ExtendedCDB 
    > field in the iSCSI Extended CDB AHS comes from SPC-3?
    The iSCSI AHS carries bytes 16-259 of a variable length CDB.
    The 2-byte AHSLength field needs to contain a value big enough
    to hold the CDB. It should be 8 less than the ADDITIONAL CDB
    LENGTH field in the CDB itself.
    > ...
    > Mike Smith
    > CTO, iReady
    Rob Elliott,
    Industry Standard Server Storage Advanced Technology


Last updated: Mon Jun 10 14:19:05 2002
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