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5.3 Levels of Backups
=====================
An archive containing all the files in the file system is called a "full
backup" or "full dump". You could insure your data by creating a full
dump every day. This strategy, however, would waste a substantial
amount of archive media and user time, as unchanged files are daily
re-archived.
It is more efficient to do a full dump only occasionally. To back up
files between full dumps, you can use "incremental dumps". A "level
one" dump archives all the files that have changed since the last full
dump.
A typical dump strategy would be to perform a full dump once a week,
and a level one dump once a day. This means some versions of files will
in fact be archived more than once, but this dump strategy makes it
possible to restore a file system to within one day of accuracy by only
extracting two archives--the last weekly (full) dump and the last daily
(level one) dump. The only information lost would be in files changed
or created since the last daily backup. (Doing dumps more than once a
day is usually not worth the trouble.)
GNU 'tar' comes with scripts you can use to do full and level-one
(actually, even level-two and so on) dumps. Using scripts (shell
programs) to perform backups and restoration is a convenient and
reliable alternative to typing out file name lists and 'tar' commands by
hand.
Before you use these scripts, you need to edit the file
'backup-specs', which specifies parameters used by the backup scripts
and by the restore script. This file is usually located in
'/etc/backup' directory. Backup Parameters, for its detailed
description. Once the backup parameters are set, you can perform
backups or restoration by running the appropriate script.
The name of the backup script is 'backup'. The name of the restore
script is 'restore'. The following sections describe their use in
detail.
_Please Note:_ The backup and restoration scripts are designed to be
used together. While it is possible to restore files by hand from an
archive which was created using a backup script, and to create an
archive by hand which could then be extracted using the restore script,
it is easier to use the scripts. Incremental Dumps, before
making such an attempt.
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