Minutes of May 9, 1996 SSC/SMC working group

tedl at exabyte.com tedl at exabyte.com
Mon May 13 14:37:29 PDT 1996

* From the SCSI Reflector, posted by:
* tedl at Exabyte.COM

Document:      96-174r0 (text version)

Fort Lauderdale, FL
Accredited Standards Committee
X3, Information Technology

To:       Membership of X3T10
From:     Edward Lappin
Subject:  Minutes of SSC/SMC Working Group Meeting
          Fort Lauderdale, FL  May 9, 1996

1.Opening Remarks
2.Approval of Agenda
3.Attendance and Membership
4.SSC Topics
  4.1   - Write Protect (different levels)
  4.2   - Read Reverse option
  4.3   - Immediate operations and reporting
  4.4   - Test Unit Ready and deferred error reporting
  4.5   - Capacity selection vs disk
  4.6   - FCP issues
  4.7   - SSA issues
  4.8   - Cleaning Log Page
5.SMC Topics.
6.Other Topics
7.Meeting Schedule

Results of Meeting

  1.Opening Remarks

       Ted Lappin, the SSC Technical Editor, called the meeting
       to order at 9:10 a.m., Thursday, May 9, 1996.  He thanked
       Adaptec for arranging and hosting the meeting.
       As is customary, the people attending introduced
       themselves and a copy of the attendance list was

  2.The draft agenda was approved.

  3.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 organization directly and materially affected
       by X3T10's scope of work.

       The following people attended the meeting:

     Name                S   Organization       Email Address

     Mr. Charles Monia   P   Digital            monia at shr.dec.com
     Mr. Edward Lappin   P   Exabyte Corp.      tedl at exabyte.com
     Mr. Ralph Weber     P   ENDL Associates    roweber at acm.org
     Mr. Pete Tobias     A   Tandem             tobias_pete at tandem.com
     Mr. Doug Hagerman   A#  Digital            hagerman at starch.enet.dec.com
     Mr. Gary Stephens   P   FSI                6363897 at mcimail.com
     Mr. George Penokie  P   IBM                gop at rchvmp3.vnet.ibm.com
     Mr. Ken Hallam      P   Unisys             ken.hallam at mv.unisys.com
     Mr. Bill Dallas     A#  Digital            dallas at zk3.dec.com
     Mr. John Scheible   A   IBM                scheible at vnet.ibm.com
     Mr. Bill Martin     A#  Hewlett Packard    wrm at core.rose.hp.com
     Mr. David Cressman  V   Quantum            dcressma at tdh.qntm.com
     Mr. Roger Cummings  O   DPT                cummings_roger at dpt.com
     Mr. Dan Strevey     V   Intellistor/       dstrevey at intellistor.com

14 People Present

Status Key:  P -  Principal
          A,A# -  Alternate
          O    -  Observer
          L    -  Liaison
          V    -  Visitor

  4.SSC Topics

     4.1    - Write Protect (different levels)
       Extensions to write protect to add new scopes and
       reporting.  In particular, write protect based on the
       following mechanisms:

           Write Protect Type            Implementation ASC/Q

           Hardware                      Exists         27/01
           Software                      Exists         27/02 (new)
           Associated (until unload)     New            27/03
           Persistent (record on medium) New            27/04
           Permanent (not erasable)      New            27/05
       Software write protect needs statement on persistence (if
       not already there).

       Associated is kept until unload or poweroff.  General
       feeling that reset should also kill it (original proposal
       has reset maintaining the write protect).

       Persistent write protect is remembered on a media unit
       basis.  Questions about what happens when the cartridge
       is placed in older drives.

       Permanent cannot be written or appended to until
       externally erased (not writable by any commands on the
       target supporting the full capabilities of the media).

       An ASCQ of 00h is any reason for write protect.

       Action to check with Gerry Houlder if disks want this

     4.2   - Read Reverse option
       Option to reverse bytes in read reverse.  Problem with
       original command option requiring reverse byte flow.  If
       make support of old form (reverse data) required but new
       hardware cannot support the old form.  How can this be
       resolved?  One way would be to have a mode bit or maybe a
       new command.

     4.3   - Immediate operations and reporting
       Current behavior makes it difficult to determine when an
       immediate operation has completed.  This proposal
       requests particular behavior using sense key specific
       time-out values in request sense for all immediate
       operations.  Need to add request sense polling
       information in each immediate command or in the model for
       immediate commands.  May want a new ASC/Q for NOT READY,

     4.4   - Test Unit Ready and deferred error reporting
       Should deferred errors be reported by Test Unit Ready?
       Text should be placed somewhere indicating whether or not
       deferred errors are allowed on TUR commands.  No mode
       page for selecting operation.

     4.5   - Capacity selection vs disk
       Do we need short tape capacity selection?  Could do this
       using single partition format with a percentage.  Bill
       Dallas thinks that we should consider using the same
       method as disk drives.

       Gary Stephens will generate proposal documents for items
       4.1 through 4.5.

     4.6   - FCP issues
       Doug Hagerman presented FCP issues regarding the profile
       for fibre channel SCSI devices.  A private loop profile
       has been started, originally for disks.

       Basic problem with FCP is that no frame-level error
       correction code is in fibre channel, only an error
       detection code.  A SCSI command maps onto an exchange.

       Error checking is on an exchange with is a sequence.
       This mechanism is part of the profile.  Initial
       justification for this mechanism came from a better error
       rate using optics but the error rate has been pushed up
       by speed and copper.  The mechanism can create command
       time-outs.  The fibre profile was built on the
       expectation that commands can be retried.

       For performance reasons, the ACK of each frame was
       removed (using class 3).  Instead, the status of the SCSI
       command implied reception and completion.
       Ordering is maintained unless a fabric (using switches)
       occurs.  In the loop profile, delivery is in order for
       frames.  But, a missing frame is a possibility.  You will
       know that you are missing a frame in a sequence but not a
       missing sequence.

       For a data sequence, each sequence is numbered uniquely
       within the command.  Not clear on what the sequence
       number requirements for the profile.
       Question:  what about the last sequence with SILI on

       Next is the question on how streaming and buffers work.
       Doug talked about cleaning up tape operation when we
       change to fibre.

       If you get an error on a write command data transmission
       error, the suggestion is that the command be resent.  The
       detection occurs during a data sequence.

       However, if all of the data cannot be stored in the
       drive, there is a problem.  Data is written to the media
       but the command has not completed.  This requires that
       the drive reposition to the start of the command ready
       for the replacement write.

       Getting into discussion about what recovery is required.
       For data transmission errors, tapes could reposition to
       allow a retransmission of the same command.  This is not
       exactly efficient.  Requires that overwrites at any point
       are possible.

       Still, the major problem is the loss of commands.  Does
       not fix the problems for printers and communication

       A poll indicates that typical applications use up to 64
       kbyte commands.

       You can always ask for the data again.  This works if
       something like the drive wants a retransmission (e.g.
       expansion of data during compression and wants to process
       the same data uncompressed) but no error occurs.

       Roger would like some tape people to come to the loop
       meeting to indicate the current error recovery.  There is
       a meeting in Santa Fe, probably Tuesday.  Need to get
       tape vendors to know about this meeting.

     4.7   - SSA issues
       John Scheible presented conversion between parallel and
       SSA.  Goal is to minimize conversion from parallel SCSI
       while gaining performance.

       SSA does have frame level retry.  A disk drive target
       implementation was able to reuse 85% of the code from
       parallel SCSI.

       Ordered delivery is guaranteed by using a single path.
       Confirmed status has been added.

       SSA is pipelined but not interlocked.  There is no end to
       end ack but there is an ack for each hop.

       Contingent Allegiance is supported by locking until the
       driver is notified.  A temporary ACA is generated by the
       protocol layer.

       Commands must use the same path if order is to be

       For hot plug, the path can be rerouted by the protocol,
       transparent to the command level.  This is possible due
       to the confirmed status.

     4.8   - Cleaning Log Page
       General agreement that a suggestion on the number of
       bytes for the cleaning log parameter is required in SSC.
       Ken Hallam wants to set the size of parameter 100h to 2
       bytes (96-155r0).

  5.SMC Topics.
       No topics were discussed.

  6.Other Topics

       No other topics were discussed.

  7.Meeting Schedule

       The next meeting of the SSC/SMC Working Group will be in
       Colorado Springs, hosted by Symbios.  Actual meeting time
       will be determined by the X3T10 Plenary.


       The meeting was adjourned at 12:50 PM. on Thursday May 9,

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