May 1995 XOR meeting minutes

Jay Elrod Jay_Elrod at
Mon May 15 08:54:14 PDT 1995

XOR Command Study Group meeting minutes - Document number X3T10/95-232r0
Meeting place: Sheraton Inn Harrisburg, Harrisburg, PA
Date: May 8, 1995


Jay Elrod  Seagate
Gerry Houlder  Seagate
Paul Hodges  IBM
Bill Hutchison  Hewlett Packard
Stephen Holmstead Hewlett Packard
Edward Fong  Amdahl
George Penokie IBM
Duncan Penman IIX
Gary Stephens  FSI
Gene Milligan  Seagate

Gerry Houlder acted as chairman for the meeting. Revision 8 of the xor
document was discussed. Below is a summary of the major issues
discussed. Note: several minor editorial changes were discussed which
are not included in this list. The next revision should be referred to if
details of these changes are needed.

1. REBUILD/REGENERATE parameter list - recent modifications were
discussed. It was recommended that  the source descriptors  be broken
out and described separately from the rest of the parameter list.

2. Annex A - recently added xor examples were discussed. No modifications
were recommended.

3. Recently added definitions section was discussed. It was recommended
that text be added which refers the reader to the appropriate document, such
as SAM and SCC, for further clarification of the meaning of the terms defined.

4. Distributed regenerate/rebuild proposal - Paul Hodges (IBM) presented more
implementation approaches for the proposal he presented at  the March '95
xor meeting. The proposal involves distributing the xor task among the source
devices involved in a regenerate or rebuild operation. The question still
stands as to whether the idea would be worthwhile from a performance
standpoint. Paul will work via the SCSI reflector to see if enough interest in 
idea exists to pursue putting it in the standard.

5. RAID 3 multicast proposal - an idea was presented (proposed off-line
by Steve Fuld of Storage Tek) for making use of multicasting capability
to streamline RAID 3 type operations during writes to an entire stripe in a
RAID 5 environment. The consensus was that the xor document is not the
proper place to standardize such an idea, since not  all physical interfaces
to which the document applies support multicasting (e.g. parallel SCSI).

6. It was strongly recommended that the "Buffer Full" ending status method
proposed in the xor document (section 1.4.1 of rev 8) be replaced by a method
which uses check condition status and a new ASC & ASCQ indicating the buffer
full condition, since getting a new status byte approved may be extremely 

7. Future plans - there was discussion regarding what the next step should
be regarding moving ahead with the xor document. It was moved that  a vote
be proposed at the plenary on Thursday for inclusion of revision 9 of the xor
document in the SCSI Block Commands standard. There was unanimous
agreement. Since neither Gerry Houlder or Jay Elrod were planning to be at
the plenary, Gene Milligan (Seagate) agreed to propose that the vote be taken.

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