XOR Comments

George Penokie GOP at RCHVMP3.VNET.IBM.COM
Thu Dec 22 08:33:22 PST 1994


Below is attached a proposal for changes to the XOR proposal.  It is based
on 94-111r2 because this is the latest document that has been distributed
to the committee.

I am concerned about the XOR working not following X3T10 procedures for
document distrubution.  It appears, from the minutes, that either a new
rev of 94-111 was distrubuted or a new proposal was distributed that
contained infromation on a new mode page and that new information was
not made available for the last mailing.

Because of the lack of documentation on this new mode page it is impossible
to say anything about it.  So although statements about there being
aggrement within the XOR meetings are good, the fact that no one outside of the
few people who were able to attend those meetings have seen it or discussed it
indicates it has not had the scrutiny it should have had.

Bye for now,
George


         Date:  Dec 21, 1994                      X3T10/95-108 rev 0


         To:  X3T10 Committee (SCSI)

         From:  George Penokie (IBM)

         Subject:  Comments on RAID 5 Support on SCSI Disk Drives
         (94-111r2)

         1-The XDWRITE command does not follow the conventions set
         down within the SPC standard.  It does not even follow the
         conventions set down within the XOR document.  I suggest the
         following (or something like this) for the XDWRITE CDB
         format:

         Byte    Description
         0       Op Code
         1       No Change
         2-5     No Change (Logical Block Length)
         6-7     Reserved
         8-9     Parameter List Length (Bytes)
         10-11   Reserved
         12-13   Transfer Length (Blocks)
         14      Reserved
         15      Control

         The parameter list would contain the secondary address and
         secondary logical block address.  Now the secondary address
         can be any size you want.  The CDB follows the same format
         as defined in the Rebuild and Regenerate commands and is SPC
         compatible.

         2-The CONTROL part of the CONTROL byte includes the Flag and
         Link bits so those bits should not appear in this proposal.

         3-The format of the SECONDARY ADDRESS field and the SOURCE
         ADDRESS field are not defined.  So I have no way of knowing
         how many bytes is enough to address all the devices. I do
         know that in SCC you can address all devices in a single
         layer with two bytes.  And since the XOR proposal is only
         addressing a single layer I do not understand why you would
         need a different addressing protocol than is already
         defined in SCC.





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