Information Technology Reference
In-Depth Information
Introduction
Given a backup requirement, you need to be able to develop a backup strat-
egy that includes scheduled backups, number of tapes required, naming con-
ventions, command protocols, and backup frequency/levels.
You also need to be able to explain how to perform incremental, full, and
remote backups to tape for an unmounted file system using the
ufsdump
com-
mand or explain how to back up a mounted file system using
ufs snapshot
.
Finally, you need to be able to explain how to perform
ufs
file system
restores and special-case recoveries.
Backup Strategies
A
backup strategy
is the procedure used to ensure that as much data as possi-
ble can be restored when a disk fails or data is accidentally deleted. There are
a number of backup strategies, each one having different strengths and weak-
nesses. The main consideration of a backup strategy is typically time—that
is, how long it takes to restore a file, set of files, a file system, or the entire
system, as well as how long it takes to perform the backups that allow this
type of restore capability. A secondary consideration is the amount of back-
up media required.
The backup strategy typically consists of a periodic full backup, supplement-
ed by a series of incremental backups.
Full Backups
As the name implies, a
full backup
consists of backing up the entire system (that
is, all the local file systems). Each file system is backed up separately. With an
unlimited amount of time and backup media, a full backup could be per-
formed every day. This would allow for a quick and clean restore as needed.
However, performing full backups every day is unrealistic. In the backup
strategy, the full backup is performed on a periodic basis, typically monthly.
This provides a baseline or starting point for backing up files that change
during the month.
Incremental Backups
Incremental backups
are used to backup files in daily or weekly increments or,
in some backup strategies, several daily and/or weekly increments. Backing
