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Finding a 4D Backup Solution Valid XHTML 1.0 Transitional

Date last modified: Sun May 21 2017 7:14 AM

'Time spent in reconnaissance is seldom wasted' - The Art of War, Sun Tzu, 400BC

This page records my researches and conclusions about backup software - primarily for Windows-based machines, and was mostly written during 2008.

What type of backup?

Which Software?

This is a list of backup software that wins my 4Dbadge 4D Backup badge, free or with a free version, which I discovered as I searched for my optimal solution:

Here are some other good backup packages which do not however count as 4D Backup solutions:

rdiff-backup: Notes on mirror + reverse incremental backup approach

rdiff-backup uses reverse incremental diffs: each time that a backup of a changed file is performed the current version of the file is retained 'clean' on the backup server (i.e. a 'mirror' of the original), a diff file is created (in a subdirectory) to allow for retrospective migration to the previous saved copy, and then the previous saved clean copy is deleted. As the file changes and is backed up over time these diff files accumulate. It is a reverse diff because it is used to go back in time to an earlier version of the file; it is incremental because in order to get a given version of the file you apply each diff file in reverse chronological sequence.

By contrast, a 'differential' rather than 'incremental' backup strategy allows recovery to any file version with only 2 sources - the 'original' and the 'differential diff' file for that version. This approach will lead to increasingly large and repetitious diff files as the current files diverge from an original, and indeed it is not a practicable solution for reverse diffs (but see below regarding LVM snapshots).

The processing of the diff files is handled by rdiff-backup 'under the hood' - the user does not have to understand what is going on. (For a utility which creates diff files and allows you to apply them manually, see rdiff, or for a way to view an rdiff-backup archive as if each historical fileset existed in full, see rdiff-backup-fs.) If a diff file is missing or corrupted for a given day then because of the incremental nature of the backups any versions of the original file for that day or for any earlier day cannot be recovered. Although this presents obvious dangers, it is at least for most purposes a safer approach than forward incremental diffs, where the corruption of one older diff will mean that more recent versions of the file cannot be recovered.

LVM

Linux's LVM2 'logical volume manager' makes the 'volume groups' (which can then be formatted to provide useable storage space) flexible and independent of the physical storage medium. Here is information about why LVM is good, and it omits to mention the availability in LVM of snapshots, which are particularly useful for making backups. [An LVM snapshot could be considered a local reverse differential backup of the corresponding volume group, but it cannot be used tout court as a long-term backup solution, only as a way of getting a temporarily-frozen fileset from which a backup can proceed. Logic suggests that a long-term LVM snapshot would get very large and impact significantly on the performance of the filesystem, and multiple snapshots would be even worse.]

LVM has the ability to 'revert' a backup: you can take an LVM snapshot, make changes to the data from which the snapshot was taken, and then revert back to the snapshot, discarding all the changes. Someone tested it here.

Useful Links

My Other Sites

My Programs

Here is a selection of some (other) programs I have written, most of which run from the command line (CLI), are freely available and can be obtained by clicking on the links. Dependencies are shown and while in most cases written for a conventional Linux server, they should run even on a Raspberry Pi, and many can run under Windows using Cygwin. Email me if you have problems or questions, or if you think I could help with a programming requirement.

Backup Utilities

Debian/Ubuntu kernel and LVM Utilities

Dellmont / Three / Giffgaff / Vodafone - VoIP and Mobile Phone Account Utilities

Miscellaneous Programs

Comments

Madpsy 30 Mar 2017, 15:45
You missed 'tarsnap' which is probably one of the best all round backup solutions for *NIX.
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