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

ddavies at ddavies at
Mon Apr 19 15:47:59 PDT 1999

* From the T10 Reflector (t10 at, posted by:
* ddavies at

Our interpretation/implementation of the information field after early
termination of a space command is to report the total number of blocks, etc.,
not spaced over (a positive number).

I remember discussions on this topic way back during the development of the
SCSI-2 standard, attempting to clarify the wording to ensure that two's
complement notation would not be used.  The only condition that 'clearly' spells
this out in SCSI-2 is when BOP is encountered in a reverse direction
(X3.131-1994, page 241, paragraph 4, last sentence).

I agree that the SSC statement prohibiting two's complement notation in the
information field for SPACE should be moved to the end of the first paragraph to
eliminate any implication about only applying to the filemark case.

Dan Davies
Overland Data

"Zeitler, Carl" <Carl.Zeitler at> on 04/19/99 06:58:22 AM

Please respond to "Zeitler, Carl" <Carl.Zeitler at>

To:   'Fibre Channel Reflector' <fc at>, 'T10 Reflector'
      <t10 at>
cc:    (bcc: Dan Davies/ENG/SanDiego/US)

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

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.


Carl Zeitler
Compaq Computer Corporation
20555 SH 249
Houston, TX 77070-2698
Room: CCA15 8 A74
Phone:  (281) 518-5258
Fax:       (281) 514-5270
E-Mail: Carl.Zeitler at 

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