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Using Martigny's optical disk drive
===================================

(Originally

     Date: Wed, 04 Apr 90 17:34:20 EDT
     From: markf
     To: switzerland
     Subject: Archiving files to the optical disks

with mods by Arthur, Jinx, and CPH.)

   There are some of you out there who would love to archive some of
your files to our optical disk autochanger, but are not quite sure how
to do it.  Here is one way to do it.

  1. Decide which optical disk you want to archive to.  Execute "bdf"
     at the shell to see which optical disks have enough space for
     you. The opticals are the filesystems that start with
     `martigny:/ac'. The "avail" column of the output lists the
     available space in 1024-byte blocks.

        Let's call the last component of the filesystem (e.g. the `4a'
     in `martigny:/ac/4a') the DISK. Call the last two components the
     ARCHIVE (e.g. `/ac/4a').

        Note that some of the optical disks are reserved for specific
     purposes.  Each reserved disk has a file `%README' in its
     top-level directory, which explains what the disk is reserved
     for.  For example, disk `1a' is reserved, and the file
     `/ac/1a/%README' contains this text:

          This directory contains the X window system sources.
          Please don't store personal files here.

  2. Create a directory on the chosen archive disk.  Execute `mkdir
     ARCHIVE/NAME', where ARCHIVE is the last two components of your
     chosen archive disk's filesystem name and NAME is some name that
     you choose to identify this archive as yours (your login name is
     not a bad choice).  Example:

          mkdir /ac/4a/markf

  3. Copy your chosen files and directory subtrees to the archive
     disk.  Execute

          cpx -vr FILE-OR-DIRECTORY1 FILE-OR-DIRECTORY2 ... ARCHIVE/NAME

     where FILE-OR-DIRECTORYN is one of the files or directories that
     you want to archive and ARCHIVE/NAME is described above.  This
     will copy all the files and the complete directory trees to the
     archive.  Example:

          cpx -vr big-file mbox src-dir scheme /ac/4a/markf

  4. Check that the copy was done.  (Only if you are paranoid.)
     Execute `ls -lR ARCHIVE/NAME'.  Example:

          ls -lR /ac/4a/markf

  5. Delete the original files.  Execute

          rm -rf FILE-OR-DIRECTORY1 FILE-OR-DIRECTORY2 ...

     I know it's scary but this must be done, it's the whole point of
     archiving.  Example:

          rm -rf big-file mbox src-dir scheme

  6. Create symbolic links to files that you archived along with a
     parallel directory structure.  (This last step is optional, but I
     find it very convenient.)  Execute

          cpx -rvs ARCHIVE/NAME/{FILE-OR-DIRECTORY1,FILE-OR-DIRECTORY2,...} .

     The idea here is to minimize disruption to you and to your
     existing directory structure (which may have contained symbolic
     links to some of the moved files).  This command will recreate
     the directories that the `rm ...' removed and it will create
     symbolic links in those directories to the files that you just
     archived.  You can now add files to those directories and do
     compilations in those directories.

        *extra-added-attraction*: I have a little emacs magic that
     checks to see if I'm trying to save a file that is a symbolic
     link and asks me if I want to overwrite the linked to file (e.g.
     the archived file).  If I say no then it will ask me if I want to
     remove the link and create the file in place of the link.  It is
     especially useful in the context of the links set up in step 8
     above.  Here is the code to add to your `.emacs' file if you want
     to have this capability:

          ;;; Don't overwrite symbolic links without asking
          
          (defun check-symlink ()
            (let* ((filename (buffer-file-name))
                   (symlink (file-symlink-p filename)))
              (and symlink
                   (not
                    (yes-or-no-p
                     (format "Symbolic link. Overwrite %s? " symlink)))
                   (not
                    (and (yes-or-no-p
                          (format "Remove symbolic link and create %s? " filename))
                         (progn
                          (delete-file filename)
                          (write-file filename)
                          nil))))))
          (setq write-file-hooks (list (quote check-symlink)))

Additional notes
================

(Originally

     Date: Wed, 4 Apr 90 18:53:39 edt
     From: Chris Hanson <cph>
     To: switzerland@kleph.ai.mit.edu
     Subject: Archiving files to the optical disks

with mods by Jinx.)

   * Available optical disks are numbered 1a, 2a, ... 16a, 1b, 2b, ...
     16b.  Note that 1a and 1b are different sides of the same disk --
     the disk must be physically flipped over (a 10-second process) to
     read the opposite side.  For now I suggest allocating only the
     "a" sides.

   * Even though the disk changer has many different disks, it has
     only two drives.  The drives are shared among the users of all of
     the disks.  Please don't copy directly from one optical disk to
     another, because this uses both drives at once; first copy from
     the source optical disk to regular hard disk, then copy to the
     destination optical disk.  Also, don't copy from one side of a
     disk to the other, as the disk will be flipped on every read and
     write (usually copying is performed in several-kilobyte chunks,
     so this quickly adds up to many flips); in addition to being slow
     this puts excessive wear on the disk and the changer.



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