(tar)Inc Dumps

incremental and listed-incremental

Full Dumps

Backups and Restoration

Using `tar' to Perform Incremental Dumps
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   Performing incremental dumps is similar to performing full dumps,
although a few more options will usually be needed.

   You will need to use the `-N DATE' option to tell `tar' to only
store files that have been modified since DATE.  DATE should be the
date and time of the last full/incremental dump.

   A standard scheme is to do a *monthly* (full) dump once a month, a
*weekly* dump once a week of everything since the last monthly and a
*daily* every day of everything since the last (weekly or monthly) dump.

   Here is a copy of the script used to dump the filesystems of the
machines here at the Free Software Foundation.  This script is run via
`cron' late at night when people are least likely to be using the
machines.  This script dumps several filesystems from several machines
at once (via NFS).  The operator is responsible for ensuring that all
the machines will be up at the time the dump happens.  If a machine is
not running, its files will not be dumped, and the next day's
incremental dump will *not* store files that would have gone onto that
dump.

     #!/bin/csh
     # Dump thingie
     set now = `date`
     set then = `cat date.nfs.dump`
     /u/hack/bin/tar -c -G -v\
      -f /dev/rtu20\
      -b 126\
      -N "$then"\
      -V "Dump from $then to $now"\
      /alpha-bits/gp\
      /gnu/hack\
      /hobbes/u\
      /spiff/u\
      /sugar-bombs/u
     echo $now > date.nfs.dump
     mt -f /dev/rtu20 rew

   Output from this script is stored in a file, for the operator to
read later.

   This script uses the file `date.nfs.dump' to store the date/time of
the last dump.

   Since this is a streaming tape drive, no attempt to verify the
archive is done.  This is also why the high blocking factor (126) is
used.  The tape drive must also be rewound by the `mt' command after
the dump is made.