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Operational and Organizational Security: Policies and Disaster Recovery• Chapter 12 737

As a backup job can fit on a single tape (or set of tapes), administrators only
need to restore the last backup tape or set that was used. Full backups will back up
everything, so additional tapes are not needed.
Incremental backups take the longest to restore. Incremental backups contain all
data that was backed up since the last backup, thus many tapes may be used since
the last full backup was performed.When this type of backup is used, administra-
tors need to restore the last full backup and each incremental backup that was
made since.
Differential backups take less time and fewer tapes to restore than incremental
backups. Because differential backups back up all data that was changed since the
last full backup, only two tapes are needed to restore a system.The administrator
needs to restore the tape containing the last full backup, and the last tape con-
taining a differential backup.
Since different types of backups have their own advantages and disadvantages,
the administrator will need to consider what type of backup is suitable to their
needs. Some types of backups take longer than others to backup or restore, so they
need to decide whether they want data backed up quickly or restored quickly
when needed.Table 12.3 provides information on different aspects of backup types.

Table 12.3 Factors Associated with Different Types of Backups

Speed of
Speed of Making Restoring the Disadvantages of
Type of Backup the Backup Backup Backup Type

Daily Full Takes longer than Fastest to restore, Takes considerably
Backups using full backups as only the last longer to backup
with either full backup is data, as all files are
incremental or needed. backed up.
differential
backups.

Full Backup Fastest method Slowest to Requires more tapes
with Daily of backing up restore, as the than differential
Incremental data, as only last full backup backups.
Backups files that have and each
changed since incremental
the last full or backup made
incremental since that time
backup are needs to be
backed up. restored.

Continued

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