Attention Tape Vendors: Intepretation of Information Field Value after Space Command early termination

Erich Oetting erich_oetting at
Mon Apr 19 10:38:15 PDT 1999

* From the T10 Reflector (t10 at, posted by:
* Erich Oetting <erich_oetting at>

The value of the Information Field after early termination of a reverse 
SPACE command was discussed at one of the SSC working group meetings.  
The SCSI-2 wording had been interpreted two different ways by tape 

1. The Information Field should contain a positive number, the number of 
blocks or filemarks not spaced over.

2. The Information Field should contain a negative number, the two's 
complement of the number of blocks or filemarks not spaced over.  
(Indicating the space was in a reverse direction.)

A rational argument can be made for either interpretation. 
After a discussion, the working group decided that SSC should specify 
that a postive number should be returned.  The SSC editor was instructed 
to make this explicit.

The above is my memory of what was done.  The SSC working group minutes 
or editors notes in SSC may indicate when the change was made.  

   ... Erich Oetting
       T10 Primary rep. for Storage Technology

Carl Zeitler wrote:
>Inserted below is the slide I showed at the FC-Tape Meeting on April 14.  I
>was asked to distribute this slide on the appropriate reflectors for
>response by Tape Vendors.  What is your interpretation of the value of the
>Information Field after early termination of a Space Command with a negative
>Count Field value (Back space)?  Please respond to the reflectors.  Thanks.
>Page 44 of SSC Document, Revision 15, 2nd paragraph, last sentence:
>A CHECK CONDITON caused by early termination of any SPACE command shall not
>result in a negative information field value.
>Change from SCSI 2.
>Current Compaq interpretation  is:
>		Forward Space:  
>COUNT field  - (blocks, filemarks, setmarks spaced over) = Information field
>		5       -			   3
>=             2	
>	Backward Space
>		-5     -			-(-3)
>=	  -2
>Is this interpretation correct?
>If correct, need to modify and clarify the above sentence.
>	Move sentence to end of first paragraph, to remove the possible
>implication that it only applies to the filemarks case.
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