X3T9.2/89-58






Date:     April 14, 1989

To:       Del Shoemaker, X3T9 Chairman



From:     John Lohmeyer, NCR Corp.

Subject:  NCR "No" Vote on SCSI-2 Letter Ballot (X3T9/89-41)

During the editing of SCSI-2 Revision 8, Larry Lamers and I 
noticed a problem in SCSI-2 that should be corrected prior to the 
SCSI-2 first public review.  Thus I am compelled to vote "No" on 
forwarding SCSI-2 to X3 for further processing.

In 8.3.3.6, pages 8-80 and 8-81, the Read-Write Error Recovery 
Page, the descriptions of the AWRE and ARRE bits are not in 
keeping with normal industry practice.  These bits control 
whether the target is permitted to do automatic medium 
reallocation when an error is encountered.

The AWRE bit enables write reallocations and the ARRE bit enables 
read reallocations.  Normal industry practice is for 
reallocations to be performed only if the data from the failing 
block is successfully recovered.  The descriptions of these bits 
permit the target to reallocate the medium even if the target is 
unsuccessful in recovering the data.  In most target designs, 
this would mean that the data is forever lost, with no 
possibility of recovery though further read attempts.

I believe that the descriptions of these bits should be revised 
as shown on the back of this page.  I have also included some 
editorial corrections.  The changes are shown by strike-out 
within braces for deletions and italics for additions.

I will gladly change my vote the "Yes" if the descriptions of the 
AWRE and ARRE bits are corrected.

  "An automatic write reallocation enabled (AWRE) bit of one indicates that 
the target shall enable automatic reallocation of defective data blocks during 
write operations.  All error recovery actions required by {bits 0-5 are} the 
error recovery bits (TB, RC, EER, PER, DTE, and DCR) shall be executed.  The 
automatic reallocation {is} shall then be performed {at the discretion of}  
only if the target successfully recovers the data in a manner similar to the 
REASSIGN BLOCKS command.  {Data is} The recovered data shall then be placed in 
the reallocated block {if the data could be recovered within the limitations 
placed on the error recovery actions (byte 2, bits 0-5)}.  Error posting as 
required by the error recovery bits shall be performed only after completion 
of the reassignment.  The reassignment process shall present any failures that 
occur during the reassignment process.  See the REASSIGN BLOCKS command 
(8.2.10) for error procedures.

  An AWRE bit of zero indicates that the target shall not perform automatic 
reallocation of defective data blocks during write operations.
  { Error recovery and error posting consistent with the error recovery 
bits(0-5) shall be performed.}

  An automatic read reallocation enabled (ARRE) bit of one indicates that the 
target shall enable automatic reallocation of defective data blocks during 
read operations.  All error recovery actions required by {bits 0-5 are} the 
error recovery bits (TB, RC, EER, PER, DTE, and DCR) shall be executed.  The 
automatic reallocation {is} shall then be performed {at the discretion of}  
only if the target successfully recovers the data in a manner similar to the 
REASSIGN BLOCKS command.  {Recovered data is} The recovered data shall then be 
placed in the reallocated block {if the data could be recovered within the 
limitations placed on the error recovery actions (byte 2, bits 0-5)}.  Error 
posting as required by the error recovery bits shall be performed only after 
completion of the reassignment.  The reassignment process shall present any 
failures that occur during the reassignment process.  See the REASSIGN BLOCKS 
command (8.2.10) for error procedures. 

  An ARRE bit of zero indicates that the target shall not perform automatic 
reallocation of defective data blocks during read operations.{ Error recovery 
and error posting consistent with the error recovery bits 0-5 shall be 
performed.}"