This file is /cdf/run1/documents/development/cdfsga_tapes.note


    Using data tapes on UNIX is different from using tapes on the VAX, 
in the following sense: the UNIX operating system does not provide 
basic tape allocate and mount commands.   We have used analysis_control
and the Computing Division rbio and ocs packages to provide
the functionality.

    Hence, as you will see from the examples, all tape commands 
are done through analysis control.  There is one advantage, the 
analysis_control commands are the same on the VAX and on UNIX.
Please see the analysis_control documentation.

    There are example jobs, which have been tested, under URL
http://www-cdf.fnal.gov/offline/cdfsga/cdfsga_examples.html


   Suggestions include:

1) As 8mm tapes are not perfectly reliable, it might be
   best to read just one tape per job.  Reading several
   tapes in a job can be problematic.

2) Writing tapes on UNIX systems in analysis_control requires the 
   use of the qualifier Output
   The command should be similar to:
      ANA>> Tape Mount/Output TAPE RK2369

3) The more files that are written on an 8mm tape, the less likely it
   is that they can be read back again.  A good rule of 
   thumb is to write fewer than 100 files per 8mm tape.

4) The analysis_control command
      ANA>> Tape Mount/Output/Overwrite TAPE RK2369
   does not work reliably, and should be avoided.

5) File names on tape need to be 17 characters or less in length,
   and in capital letters.  This is the ANSI and CDF standard, but
   I have encountered CDF-VAX tapes which do not follow this standard.

6) The RK series of tapes stay in the vault in the Feynman Center.  
   The RK series of tapes are already labelled.  
   Video Grade tapes are RK0001 to RK6999.  
   Data Grade tapes are RK7000 and up.

   If you would like to reserve a blank tape from the RK series of tapes,
   please use the CDF Tapes Database, available on the World Wide Web 
   at the following URL:

   http://www-cdf.fnal.gov/internal/tapes/tapes.html

7) Avoid using a wildcard syntax in file names on tape, as this
   sometimes reads junk files which are on the tape.  Use
   specific file names instead.

8) You can get information about pending tape mounts with the commands
      > setup ocs
      > xocs &
      Click on View
      Select Mount Requests
   This is quite useful to see when the mount request went in,
   and when it was satisfied.

9) You can see which drives are allocated, and to whom with the ocs commands
      > setup ocs
      > xocs &

10) ocs is documented in PostScript format in file
      $OCS_DIR/doc/reference.ps

11) It is possible to leave 8mm drives allocated on cdfsga,
   especially if the drastic
      > kill -9 <pid>
   or
      > qdel -9 <request-id>
   commands are used, instead of the gentler
      > kill -17 <pid>
   and
      > qdel -17 <request-id>
   commands.    Please check from time to time to see if drives have
   unintentionally been left allocated by you.

   In order to dismount and deallocate the drives, please
   use commands similar to

      > setup ocs
      > ocs_devfile -t cdf11
      /dev/rmt/tps6d2nrnsv.8500
      > mt -t /dev/rmt/tps6d2nrnsv.8500 rewind
      > mt -t /dev/rmt/tps6d2nrnsv.8500 unload
      > ocs_deallocate -t cdf11

12) Sorry to mention this final point, but it has occurred,
    so I'll discuss it briefly here.  Please try to read the files 
    on the tape in the order that the files are on the tape.  Generally 
    speaking, reading the files in reverse order will not work.



   Finally, here is a request:

   If you obtain a "Read label failed" error message similar to:
      OCSERR: Read label failed for /dev/rmt/tps6d4nrnsv.8500 with errno=5
   please report this to cdfsga-team@fnal.gov 
   making sure to include the exact text of the full error message (as above)
   in your report.

   These errors seem to pressage the drive breaking down,
   and so we would like to know about these errors.