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I've got relatively big filesystem (ext4) with lots of small files and I'd like to backup it. Making full backups often is not feasible to me so I want to have a way to make differential/incremental backups (differential preferred).

But... this is laptop, and scanning for changed files takes lots of time. My questions:

1) Is it possible to get list of files changed since some date from ext4's journal? I know it wasn't designed with this idea in mind, and it might be too small for bigger timespans, but maybe it is somehow possible?

2) Is it possible to monitor filesystem modifications and maintain a list of changed files reliably? I think I could use inotify, but this might be too slow to monitor full filesystem and might be unreliable. (by reliable I mean either I get all modifications since last backup (and this list is not missing anything) or an error message).

Laptop runs Debian unstable.

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Not an answer for your platform, but Apple's FSEvents does exactly this; arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/7 Maybe you can find substitutes knowing that name now. –  Arjan Mar 20 '10 at 14:04
inotify is one of them. –  oKtosiTe Dec 1 '10 at 19:58

2 Answers 2

Isn't rsync the best method? This tutorial is excellent.

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rsync needs to scan full filesystem (ie. check every file's metadata) to check which files changed, and this takes lots of time on my laptop. I'd like to avoid that scan. –  liori Jan 8 '10 at 22:26
Oh I see. I know zfs supports this, but I don't think ext4 does. Does OpenSolaris run on your laptop? :o) breden.org.uk/2008/05/12/… –  Iain Jan 8 '10 at 22:48
No, Debian..... –  liori Jan 8 '10 at 23:53

You could use this approach.

This is a tutorial for creating a Dropbox clone using inotify, rsync and lsyncd.

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lsyncd assumes synchronization after every change, and I'd like to sync only once a day (my backup space is external to the laptop). –  liori Jan 9 '10 at 13:36
In this case, just use cron instead of lsyncd ? The hard part is not this one, but setting up inoty to watch your changes without hitting performance issues. –  Julien Nicoulaud Jan 9 '10 at 20:49

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