Minutes of May RAID Study Group Meeting

John Lohmeyer jlohmeye at ncr-mpd.FtCollinsCO.NCR.COM
Thu May 26 14:13:21 PDT 1994

Minutes for RAID working group 5/17/94
Accredited Standards Committee
X3, Information Processing Systems
                                                      Doc. No.: X3T10/94-108r0
                                                          Date:   May 17, 1994
                                                     Ref. Doc.:
                                                      Reply to:     G. Penokie

To:         Membership of X3T10

From:       George Penokie and Ralph Weber

Subject:    Minutes of RAID Working Group Meeting
            May 17, 1994


 1.    Opening Remarks
 2.    Attendance and Membership
 3.    Approval of Agenda
 4.    Report on last RAID Working Group
 5.    Procedural and Process Notes
 6.    SDA Commands and Mode Pages (94-042r4)
 7.    SDA States and Types (94-041r4)
 8.    Dual-Controller Issues
 9.    SCSI Disk Array Model (94-040r4)
 10.    Mandatory/Optional RAID Requirements
 11.   Action Items
 12.   Meeting Schedule
 13.   Adjournment

                               Results of Meeting

1.    Opening Remarks

George Penokie the RAID Working Group Chair, called the meeting to order at
9:08 am, Tuesday, May 17, 1994.  He thanked AMP for hosting the meeting.

As is customary, the people attending introduced themselves.  A copy of the
attendance list was circulated for attendance and corrections.

It was stated that the meeting had been authorized by X3T10 and would be
conducted under the X3 rules.  Working group meetings take no final actions,
but prepare recommendations for approval by the X3T10 task group.  The voting
rules for the meeting are those of the parent committee, X3T10.  These rules
are:  one vote per company; and any participating company member may vote.

The minutes of this meeting will be posted to the SCSI BBS and the SCSI
Reflector and will be included in the next committee mailing.

George stated that this is the 19th meeting of the RAID study group and the
6th joint RAID Advisory Board/RAID working group meeting.  The purpose of the
group is to deal with interface issues related to using RAIDs.  The study
group will assess the issues and then formulate a strategy for dealing with

2.    Attendance and Membership

Attendance at working group meetings does not count toward minimum attendance
requirements for X3T10 membership.  Working group meetings are open to any
person or company to attend and to express their opinion on the subjects being

The following people attended the meeting:

                      RAID Study Group Meeting Attendees

                                                      Phone Number -or-
         Name          S       Organization         Electronic Mail Address
---------------------- - ------------------------- -------------------------
Mr. Larry Lamers       A Adaptec                   LJLamers at AOL.com
Mr. Ken Scherzinger      Amphenol Spectra-Strip
Mr. Randy Hall           Array Technology          hall at arraytech.com
Mr. Jerry Fredin       A AT&T/GIS                  Jerry.Fredin at WichitaKS
Mr. George Su            CMD Technology            714-454-0800
Mr. Allan Cole           CORE International        73532.1636 at compuserve.com
Mr. Bill Dallas        A Digital Equipment Corp.   dallas at wasted.enet.dec.com
Mr. Doug Hagerman      A Digital Equipment Corp.   hagerman at starch.enet
Mr. Paul Massiglia     O Digital Equipment Corp.   massiglia at genral.enet
Mr. Ralph Weber        A Digital Equipment Corp.   weber at star.enet.dec.com
Mr. David Race           DPT
Mr. Dal Allan          P ENDL                      250-1752 at MCImail.com
Mr. Howard Grill         Formation                 609-234-5020
Mr. Bill Hutchison       Hewlett Packard Co.       hutch at .boi.hp.com
Mr. Paul Boulay          Hitachi Computer Products 408-986-9770
Mr. Giles Frazier      A IBM Corp.                 gfrazier at ausvm6.vnet
Mr. Paul Hodges        A IBM Corp.                 phodges at vnet.ibm.com
Mr. George Penokie     P IBM Corp.                 gop at rchvmp3.vnet.ibm.com
Mr. Dick McCormick       Peer Protocols            714-476-1016
Mr. Gerald Houlder     A Seagate                   gerry_houlder at notes
Mr. Gene Milligan      P Seagate                   gene_milligan at notes
Mr. Joe Argento          Seek Systems
Mr. Vit Novak          A Sun Microsystems, Inc     vit.novak at eng.sun.com
Mr. Robert N. Snively  P Sun Microsystems, Inc     bob.snively at eng.sun.com

24  people present

 Status Key:  P   -  Principal    ** X3T10 status still being defined
              A   -  Alternate
              O   -  Observer
              L   -  Liaison
              S,V -  Visitor

3.    Approval of Agenda

The agenda developed at the meeting was approved.

4.    Report on last RAID Working Group

Last RAID Working Group was held in Bellevue, WA.  Several members of the RAID
Advisory Board were present.  George stated that the minutes of the Bellevue,
WA meeting have been published on the SCSI Reflector.

5.    Procedural and Process Notes

George announced that the SCSI-3 Controller Commands (SCC) project proposal
has been approved.  This means that the X3T10 study group now is a working
group.  It also means that the working group can take proposals to the X3T10
Plenary meeting for votes.  The details of this process were discussed.

The group discussed which RAID documents could be voted on at the Thursday
Plenary meeting.  George was certain that the addressing document could be
voted on, because it has not changed for months.  He was less confident that
attempting to vote on the model would survive a two-week-rule challenge.

George announced that he has converted to using Frame Maker.  There was a
brief discussion of how document distribution and interchange will be handled
in this environment.

The group discussed the best approach for getting the document through the
X3T10 voting process.  George is anticipating a vote for a forwarding letter
ballot at the September Plenary.  Dal suggested an introductory session at
either the July or September Plenary.  George said that he may not be able
to prepare the introduction and do the necessary editing by July.  George was
more comfortable with doing the introduction in September.

6.    SDA Commands and Mode Pages (94-042r4)

George presented a revision to the document defining the new commands and mode
pages needed to implement SCSI disk arrays (X3T10/94-042r4).  While trying to
assign SCSI op codes to the new commands, George decided that too many SCSI
commands would be required.  So, George grouped the commands into four groups:
a single SCSI op code.  A Service code field is defined in each SCSI CDB
giving the full array command set, as previously defined by the group.

Questions were raised about whether different Service codes cause a single
SCSI op code to either transfer data in or out.  George said that the data
transfer direction would depend on the Service code.  Bob Snively requested
that data transfer direction be defined by the SCSI op code.  George agreed to
break the op code by data transfer direction, yielding: MAINTENANCE IN,

George began discussing the individual op-code/service-code commands.
Questions were raised about the extensibility of some fields.  George, Doug
Hagerman, and several others agreed to consider extensibility after the basics
of the command set have been determined.

George described every command and its parameters.  Questions of detail were
raised for a few commands.  George was asked to increase the reserved space in
the headers of the parameter data on several commands.

Toward the end of the review, Giles Frazier complained about the usage of
command to name a CDB whose function is qualified both by op code and service
code.  George agreed to consider a name that uses the word "service" instead
of "command."

In Table 51, several important concepts were raised.  P-extents should be
rebuilt from a specific redundancy group or from an SDA selected (any)
redundancy group.  The specific/any distinction should be selected using a
bit.  The parameter data should contain only one R-LUI per P-extent.  Doug
Hagerman reminded the group that the P-extent (in this case) may cover several
redundancy groups (because the P-extent is a free-form command parameter).
Ultimately, this led to the realization that the original Rebuild P-Extent
parameter list format was correct.

As the discussion continued, George put more red ink on the Table 51 slide
than on any previous slide.  The specific needs of the rebuilding operations
involving multiple redundancy groups (that may overlap) produced several
conflicting definitions.  A major concern was whether the rebuild command
would fail when a redundancy group could not be rebuilt.

Dal Allan proposed two versions of the rebuild: 1) rebuild all and 2) rebuild
all except.  Both of these provide a paradigm that allow the SDA to report an
error if the rebuild cannot be completed.  Dal noted an additional model;
rebuild everything that can be rebuilt using this list of redundancy groups.
This most closely matches the command, as originally proposed.  However, it
can be viewed as incomplete because the SDA cannot report a failure to perform
the rebuild.  The SDA gets into this trap because it must assume that the host
intentionally omitted the redundancy group(s) that prevented the complete

The group agreed on the following rebuild operational rules:

  a) all assigned space within the P-extent shall be rebuild,
     otherwise there is an error
  b) the ways of specifying the redundancy groups to be used are:
     1) rebuild with ALL redundancy groups (if overlaps, use ALL)
     2) rebuild with ANY redundancy group (if overlaps, use ANY one)
     3) rebuild with all redundancy groups, except those listed (if
         overlaps, use ALL)

During a discussion of continuous verification of V-LUI ranges, George noted
that there is no way to report if continuous verification is enabled.  For a
few brief moments, George was ready to add reporting to one of the report
commands.  Then, the complexity of that hit home, and George said that no
reporting would be provided.

7.    SDA States and Types (94-041r4) Penokie

George presented the 4th revision of the SDA States and Types document.

George noted that the Readying bit is an or condition of the states of all
logical units on the SDA.  George also noted several reporting situations
where the exact nature of the reporting methodology is vendor specific.

George was asked to define a command that returns states of all addressable
things in an SDA.  The command needs to return lists of states.  George agreed
to develop the details before the next meeting.

In the set of redundancy group states, George agreed to add a new state,
Invalid Protected Space.  Invalid Protected Space means that the protected
space is no longer intact.

George noted that he removed the Exposed state from the set of spare states.
Spares cannot be in the exposed state.

8.    Dual-Controller Issues

Jerry Fredin (AT&T/GIS) presented a collection of questions regarding how the
SDA model applies to dual-controller configurations.  His first question
concerned how paths into the controller are addressed.  When a controller
(or DACL) fails in a redundant configuration, how does that failing unit get
identified for maintenance personnel?

The discussion turned to using the get states command (described above).
Ralph proposed definition of a new state for controller C-LUIs, I'm talking to
you (ITTU).  Used in combination with the get states command, the ITTU state
allows a host to map relationships between multiple-controller C-LUIs and the
addresses that it asserts to get to them.  This would further help
reconfiguration because it would allow the host to quickly build commands that
have the effect of saying, "Provide access to R-LUI five through the C-LUI
that I'm talking to."

The group also discussed some kind of "Instruct C-LUI" command.  This was felt
to be a sub-command the MAINTENANCE commands.  Ralph proposed a command format
that George will consider.

9.    SCSI Disk Array Model (94-040r4)

George reviewed changes to the SCSI Disk Array (SDA) model.  The changes were
minimal, but George still received some comments about them.

10.    Mandatory/Optional RAID Requirements

The group discussed the process by which they will define what commands and/or
features are required for SCSI Disk Arrays.  The need for very simple
implementations (that don't do everything) was discussed.  However, there also
is a market need for more complex implementations.  No resolution was reached
on the specific requirements.  George expressed a preference for resolving the
mandatory/optional issues at a future meeting.  Doug pushed for simplicity;
ideally all commands mandatory.  Dal proposed dividing implementations into
configurable and non-configurable.  George agreed that an INQUIRY data bit
would be defined to segregate configurable and non-configurable DACLs.

11.   Action Items

  a) Penokie    Revise the SDA Commands and Mode Pages (94-042) document based
                on comments and discussion topics from the meeting.
  b) Penokie    Define a command for returning states (see notes in the SDA
                States and Types discussion).
  c) Penokie    Revise the SDA States and Types (94-041) document.
  d) Penokie    Roll SDA Model, SDA Commands and Mode Pages, and SDA States
                and Types in to a single document.
  e) Hagerman   Propose ASC/ASCQ definitions for RAID.  Said proposal must be
                sent to X3T10 for approval and inclusion in the SPC.

12.   Meeting Schedule

The next meeting of the RAID Study Group is planned for June 21, 1994 at the
Sofitel in Minneapolis, MN.  The meeting is expected to run from 9:00am -
5:00pm.  This meeting will be a joint RAID Advisory Board Host Interface
Group and X3T10 RAID Working Group meeting.

13.   Adjournment

The meeting was adjourned at 5:31 pm. on Tuesday, May 17, 1994

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