Page 1326 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Using Backups

In case of system failure, many companies use one of two common
methods to restore data from backups. In the first situation, they
run a full backup on Monday night and then run differential
backups every other night of the week. If a failure occurs Saturday
morning, they restore Monday’s full backup and then restore only

Friday’s differential backup. In the second situation, they run a full
backup on Monday night and run incremental backups every other
night of the week. If a failure occurs Saturday morning, they
restore Monday’s full backup and then restore each incremental
backup in original chronological order (that is, Wednesday’s, then
Friday’s, and so on).

Most organizations adopt a backup strategy that utilizes more than
one of the three backup types along with a media rotation scheme.

Both allow backup administrators access to a sufficiently large range
of backups to complete user requests and provide fault tolerance while
minimizing the amount of money that must be spent on backup
media. A common strategy is to perform full backups over the
weekend and incremental or differential backups on a nightly basis.
The specific method of backup and all of the particulars of the backup
procedure are dependent on your organization’s fault-tolerance

requirements. If you are unable to survive minor amounts of data loss,
your ability to tolerate faults is low. However, if hours or days of data
can be lost without serious consequence, your tolerance of faults is
high. You should design your backup solution accordingly.

The Oft-Neglected Backup

Backups are probably the least practiced and most neglected
preventive measure known to protect against computing disasters.
A comprehensive backup of all operating system and personal data
on workstations happens less frequently than for servers or