FILE MAINTENANCE POLICY

   This SAILON describes file dumping, restoring, and purging
policies for the PDP-6/10 system.  The goal of these policies
is to distribute the available disk storage in accordance with
research needs, to provide sufficient backup so that users will
not find it necessary to save their own files, and to aid them
in restoring files that may have been garbaged.



DUMPING
   There are two types of dumps; incremental and full.
Full dumps put all files on magnetic tape and are done once
a week and just before purging.  All full dumps will be saved
for approximately six months and selected ones will be saved 
for three years.
   Incremental dumps save all files that have been created or
changed since the last full dump.  The incremental dump will
be done daily and will save back to the previous full dump.
Incremental dumps will be kept two weeks.
   Whenever the disk is wiped, it will be restored from the
last full dump and the last incremental.  The relevant infor-
mation (date-time of roll-back and date-time of restoration)
will appear in the message of the day for several days.



RESTORING
   If for some reason a user must restore his files from the
magtapes, the procedures are as follows:

   1. RESTORING FROM THE FULL DUMP.
    A)   To find the magnetic tape that you need, look in the
     black loose-leaf binder labeled "DAEMON FULL DUMPS" locat-
     ed in the bookcase between the two magtape racks in the 
     computer room.  The date that the dump was made is written
     on tle separation cards between the dump listings, and the
     date and time is written on the first page of the dump 
     listing.
    B)   After you have found the tape bearing the files that 
     you wish to restore, return the black binder to the book 
     shelf.  The tapes are located in the magtape racks to the
     right of the bookcase.  The tapes are dentified by separ-
     ation cards.  The tapes are numbered from one(1) to what-
     ever number was required to complete the dump.  Select the
     magtape that you need and mount it on a magtape drive.
    C)   Begin the restoration by typing the command "RESTORE
     FROM MTAn"(mta0 is assumed if only "RESTORE" is given).
     This command will cause the "daemon" program to search
     the magtape and restore all of the files that are on the
     tape under the project-programmer number which you logged
     in under.  If you want to restore only a certain file, 
     type the command "RESTORE <file>,<file>,<file>,...",etc.
     The restore command is described in section 1.B.11 in
     chapter 1 of the Monitor Manual (SAILON NO.54).  As each
     file is restored its name will be typed out.  When the 
     restoration is complete, the user must halt the tape or
     it will continue to search the tape for other files 
     under that project-programmer number.  To halt the tape
     after the last file has been restored, type "CONTROL C",
     and then type "REWIND".  After it has finished rewinding,
     the tape should be replaced in the rack.  If the user has 
     specified the name of the file or files that he wants re-
     stored in the command string, the program will automatic-
     ally exit and return to the monitor.  After restoring the
     last file, please return the tape to the rack.

POINTS TO REMEMBER:
  1. Immeadiately return the black binder to its place on the
   bookshelf, someone else may need to use it.
  2. No write-ring is needed in the magtape reel in order to
   restore files.
  3. After restoring, be sure to rewind the tape and return 
   it to its proper place on the tape rack.
    
 
    2. RESTORING FROM AN INCREMENTAL DUMP.
         If the particular file or files that you are restoring 
      has been accessed or innovated since the time of the last
      full dump, these innovations can be restored to the disk
      by restoring from a daemon incremental dump.  The incre-
      mental dumps can be found in the black binder labeled
      "INCREMENTAL DUMPS".  The incremental dumps are entered so 
      that the most current dump is the first dump encountered in 
      the binder.  The incremental dump tapes are located on the 
      fourth and fifth shelves from the top of the magtape rack
      nearest the magtape drives, the most current dump being the 
      one to the immediate left of the empty tape canister.  The
      restoration procedure is identical to that used for the full
      dump.



PURGING
   About eighty percent(80%) of the disk will be allocated to file
storage for authorized users.  The allocation will vary with the
 programmer but will typically be 150k words per person.  When-
ever the disk utilization exceeds a certain value(~95%), the
disk will be dumped and purged as follows:
   1. All files associated with unauthorized users will be purged. 
   2. Files associated with an authorized user that exceed his
     allocation will be trimmed back to the allocation by delet-
     ing, in order, files having the following extensions:
             A) .TEM, .TMP	
             B) .LST
             C) .DMP
             D) .REL
             E) all others.
     Within a given category, files will be purged in order by 
     date, oldest first.  Note that if the user has a recent file 
     that is larger than his allocation, this procedure may 
     purge all his files.

   To avoid certain kinds of astonishment, the files of users who 
   are logged-in will be exempt from purging.