Module Release February 2004: Backing Up

This month's offering completes the cycle of LPI Level 1 course modules, by covering system back-up, its objectives, its strategies and the major tools employed.

LPI Objective 2.211.3 (“Backup operations”) simply asks you to:

“create an offsite backup storage plan”

Before you can create such a plan, you need to consider is why you need it, e.g., to cope with disk failure, corruption by software bugs, configuration mistakes by administrators, accidental deletion or overwriting, malicious deletion or virus attack, theft, fire, etc.

Your assessment of comparative risks and resources will influence the selection media types and back-up sites employed. Most organisations will combine several options (e.g., tape, hard disk, on-site and off-site) to cover different requirements.

Traditionally we think of three main back-up types: full (includes everything of importance), differential (e.g., nightly backup which only include files changed since the last full backup) and incremental (typically only includes files changed in the last 24 hours).

Your backup strategy is largely built around choices about the use of these three types, e.g., choosing which files to include, choosing the frequency of with which each back-up type is made, choosing the length of time that each type is stored, etc.

Which ever medium or strategy is chosen, tar remains the key Unix tool for creating, interrogating and restoring back-up archives, so the core of this module provides considerable detail on its usage. Other tools covered include mt (for controlling tape drives), cpio/afio (alternative archivers to tar), dump and restore (allowing direct access to the filesystem, rather than through the kernel).