Backups

Backup Types
There are three basic types of backups: full, differential and incremental. A complete/whole/full backup makes a copy of all the files of the set to be backed up (such as your home directory, or your web site, or a complete filesystem). “Incremental” and “Differential” backups are used to minimize the amount of time for a backup, repetitive backups, and space on a disk.

What is an incremental Backup?
An incremental backup is a partial backup in that only the files which have changed since the last backup (full, or incremental) will be copied. Consequently, a series of incremental backups needs to be preceded by a full backup. All backups are kept for a possible need to restore the data (restore: the reverse of a backup). Restoring to a certain point in time requires locating the last valid full backup and all the incremental ones that followed, up to the particular point in time where the system is supposed to be restored. This model offers a high level of security that something can be restored and can be used with removable media such as tapes and optical disks. The inconvenience is dealing with a long series of incrementals and the high storage requirements.

What is a differential Backup?
A differential backup is also a partial backup, but differs from an incremental one in that the files to be copied are the ones which have changed since the last full backup; this means that the list of files increases with time, and each differential backup is larger than the previous. Its advantage is that a restore involves recovering only the last full backup and then overlaying it with the last differential backup. The disadvantage is that each day elapsed since the last full backup, more data needs to be backed up, especially if a majority of the data has been changed.


 * Source: Wikipedia

For most home users, not professional, making differential backups is the best alternative. Starting with a full/complete backup and followed by a full/complete weekly, monthly or whatever is required. The best time for a complete backup is reached when the differential backup becomes too large. The disadvantage is the file for differential backup will be always overwritten. The advantage is that it saves time and space.

Important Considerations
When you're making your backup, you don't want the filesystem changing while you're copying it (this can lead to problems). You should only run a backup on a partition that is either unmounted or mounted read-only. This means you may have to either:


 * Reboot with a live-cd, and running dd on your unmounted partitions
 * Go into single user mode and remount the partition in read-only mode

A short example:

init 1 umount /home && mount -o ro /home
 * 1) Go into single user-mode
 * 1) Remount /home read-only

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