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Performing a combination of full and partial backups on a daily
basis provides you with file security. As system manager, you decide what
type of backup to use and how often to perform each one.
In many companies, for example, the system manager schedules
full backups once per week and one of two kinds of partial
backups, an incremental partial backup or a cumulative partial backup,
all other days to save time and decrease media usage. The purpose of a full system backup is to store your entire
system (files, data, and programs) to tape. Depending on your needs,
you will want to do a full system backup at least once a week, and perhaps
more often.
During an incremental backup, you make a backup copy of only those
files that have been modified on or after a specified date. Typically,
this is the date of the last backup, regardless of whether it was a partial
backup or a full backup. If you back up your system on a daily basis, each
incremental tape will contain those files updated during the last 24 hours.
During a cumulative backup, you make a backup copy of all files that have
changed since the last full backup, so that the number of files copied to
tape accumulates. If you back up your system on a daily basis, the first
cumulative tape will contain files updated in the preceding 24 hours, the
second tape contains files updated in the preceding 48 hours, and so on.
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