Archiving data

NOTE: if the DECstation power is interrupted, or if the DECstation is rebooted, the exabyte will rewind. If you then write to the tape without positioning it at the end-of-tape, you will overwrite any existing data.

• Load an exabyte tape into the CX-peripherals exabyte tape drive. This is done by gently pushing the eject button, waiting a few seconds (or longer if there is already a tape in there which has to rewind) for the door to open, and loading a tape in such a way as the writing on the tape is right-way up (if writing to the tape, don't forget to push the write-inhibit flag on the tape so that it isn't showing red). Close the door gently by hand. Wait about 2 minutes for the tape to automatically load and come on line, when the flashing green light becomes constant.
• On the DECstation, cd to /data0 or wherever the images have been put. If you have a new tape, with no existing data written on it, type:

  tar cvf /dev/nrmt0l im* log.txt

  This will slowly and verbosely archive all the images im001... and the log file to tape. A night's data of 100-200 images may take 5-10 minutes. If we only wanted to archive from im100 onwards, replace the im* with im1??. The questions marks act as single-character wildcards. Note the above command does not rewind the tape, so more images can be added later to the rest of the tape.

• You can list what images are on the first tar saveset on a tape by doing:

  mt rewind
  tar tvf /dev/nrmt0l

  Note that the tar command does not rewind to the beginning of tape after listing the files, so you are ready to write the next saveset, while leaving the saveset just listed intact, i.e., using ``tar tvf'', you move to the end of the saveset listed, protecting it when you put more data on tape with ``tar cvf''.

  WARNING Using tar, it is easy to overwrite your precious data. In particular, if you rewind and do a ``tar cvf'', tar will happily overwrite any previous saveset without asking. The lesson is: Always use the tar tvf option to check what is on tape if you are uncertain of the tape position. Don't forget: the tape is rewound after a power failure or if the workstation is rebooted.

  NOTA BENE If you do a tar tvf and get a warning message that blocksize=0, DON'T PANIC. Tar will put blocksize=0 savesets between savesets written by successive use of tar cvf. Just keep using tar tvf until you get two messages in a row that blocksize=0, then you are at the end of the tape, and can write more data. If you see a message that says something like ``saveset continues on next tape, press return'', then use CNTL-C to quit ``tar'' and then use ``mt -f /dev/nrmt0l bsf 1'' to move back by one filemark. The tape should then be ready for the next saveset to be written.