Backup from GNU/Linux to NAS4Free (to separate hard drives)

Question

I have a NAS that runs NAS4Free. It has two hard drives (formatted as UFS), which run separately (so no RAID/JBOD).
On one hard drive, I want to backup my audio and video files, and on the other hard drive all my other files (text files, PDFs, images, etc.).

The files that have to be backed up all come from a single computer, running GNU/Linux. For this computer, I’m looking for a backup software (must be FLOSS) that, after configuration, automatically sends the files to my NAS (to the correct hard drive, depending on my initial configuration which folders should go to which drive).

My NAS does not necessarily run 24/7, so the backup software should be able to handle this. Being able to pause/cancel a current backup process would be useful.

Only files that were changed should be transferred (and ideally only the changes, not the whole files). Note that even my binary files might be changed, e.g., when tagging music.

On the NAS, I want to be able to access previous versions of the files, and ideally each backup on the NAS (e.g., in date-based folders) would consist of all files, by making use of hard links. So for (manually) backing up my backup, I could copy a specific date folder from the NAS to an external drive, and then have all my files (as from that date).

If I need to restore something, I’d like to be able to retrieve it manually (e.g., by SSH-ing into the NAS), so that I’m not bound to using this backup software. However, the backup software might also offer a more convenient way to access (or even rollback) files, as long as it’s optional.

I won’t use encryption (storage as well as transfer can be unencrypted).

Answer 1

^{Note: I have not used any of the following products myself, and thus usually would be unsuited to write an answer. I do so only on special request of the OP.}

I've done a little search and found e.g.

• A Howto on Scheduled Backups With Rsyncbackup On Debian Etch
• A detailed article on Incremental Backups on Linux (using the rsync/hardlink approach).
• Finally, I've found a Python script on Github which looks quite promising – provided you have Python available.

All three approaches make use of tools already available on a Linux machine, mainly rsync and, in some cases, the simple copy (cp) command. The idea behind this is easy:

• rsync copies only changed files (minimizing overhead)
• rsync --delete allows to remove files no longer existing
• on the target, multiple "generations" are maintained using multiple directories
• across generations, hard links are used for unchanged files, minimizing use of disk space

So this would match your requirements:

• runs on Linux: yes
• free and open-source: yes
• covers unavailability (no 24/7): up to you to check the return codes. The Python variant e.g. tries the target machine via ping first, so your Cron script could e.g. start with something like (pseudo-code): "while [[ $(ping -c 1 nas) -ne 0 ]] { sleep 360; exit after 10th try }" – i.e. trying to ping the NAS 10 times in 5min intervals (or whatever you find suiting) to make sure it's available.
• access previous backup generations: yes (you configure how many)
• all files (using hard links): exactly :)
• no special software for restore: nope, simply copy it via e.g. SSH

As written initially, I have not tested these specific setups. But from using this concept in some of my own scripts, I'm confident this is a solution suitable to you.