If you think you use Linux and don’t need any of this, you are wrong. There’s precious little Linux can do to restrain your hard disk failure. If the disk goes down, Linux goes down with it, and depending upon the situation, Linux would perhaps care to tell you that something is drastically wrong. So with the need for backups firmly established, let’s look at what Linux provides in terms of support for backing up and recovering data from backups. Note that any situation, which implies loss of data, is termed a "disaster".

Linux, like every other flavor of Unix, provides the basic data archiving utilities like tar, cpio, and dd, used for backing up data on tapes. Linux also provides an implementation of software RAID that provides up to level 5 support. Armed with this information, let’s see how we can plan for backups and disaster recovery.

First, what is your environment? Is the MTTR (Mean Time To Repair) very critical that it must be kept the lowest? Depending on these, you would choose to implement hardware RAID with at least levels 0 and 1. Hardware RAIDs come with hot disk swap capability; such a solution is expensive but gives you literally zero down time. An alternate to such a system is software RAID implementation that functionally eliminates service interruptions due to disk failures by making use of the mirrored disk and keeping the services going. However, the absence of hot swap capability would require that the system is shut down, the disk replaced, synchronized with the mirror disk and the services started up. This down time could be during the lean service hours. The least expensive solution with the longest MTTR is using tapes for restoring the data onto a new disk.

It’s important to understand that there must be made a clear demarcation of the data on the system into system data—data used for configuring system services like printers, network, kernel, etc, and user data—data generated by users. Typically, system data is not expected to change very often (except system logs) and does not, whereas user data does change daily. So one would handle this by backing up the user area, possibly every day, and the system data less frequently. Backing up itself is done in two possible ways: complete or full backups and incremental backups. As the name suggests, incremental backups record changes that have occurred since the last full backup.