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

When making backups, the administrator needs to decide what data will be
copied to alternative media. Critical data, such as trade secrets that a business relies
on to function, and other important data crucial to a business’ needs must be
backed up. Other data, such as temporary files, applications, and other data may not
be backed up, as they can easily be reinstalled or missed in a backup. Such deci-
sions, however, will vary from company to company.
Once the administrator has decided on what information needs to be backed
up, they can determine the type of backup that will be performed. Common
backup types include:

■ Full backup, which backs up all data in a single backup job. Generally, this
includes all data, system files, and software on a system.When each file is
backed up, the archive bit is changed to indicate that the file was
backed up.

■ Incremental backup, which backs up all data that was changed since the last
backup. Because only files that have changed are backed up, this type of
backup takes the least amount of time to perform.When each file is
backed up, the archive bit is changed.

■ Differential backup, which backs up all data that has changed since the last
full backup.When this type of backup is performed, the archive bit is not
changed, so data on one differential backup will contain the same infor-
mation as the previous differential backup plus any additional files that
have changed.
■ Copy backup, which makes a full backup but does not change the archive
bit. Because the archive bit is not marked, it will not affect any incre-
mental or differential backups that are performed.
Because different types of backups will copy data in different ways, the methods
used to back up data vary between businesses. One company may do daily full
backups, while another may use a combination of full and incremental backups (or
full and differential backups).As will be seen in later sections, this affects how data
is recovered and what tapes need to be stored in alternative locations. Regardless of
the type used, however, it is important that data is backed up on a daily basis, so
that large amounts of data will not be lost in the event of a disaster.

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