Dale Forester's questions

In my research on file versioning at the fs level, snapshotting, and related ideas, I took a look at hard-links and exactly what they are and how they behave. Using rsync you can get a pretty slick poor man's snapshotting system up and running on file systems that don't natively support it.

But, can you get immutable hard links on ext3/4 or any other file systems for that matter?

My definition for immutable hard link is: A hard link which, when changed on one location, becomes a regular copy and no longer a hard link.

I would like this because it would enable snapshotting use of the source data to link against instead of a copy of the data (in the case of the rsync snapshotting technique).

I have gigabytes of data that can't be duplicated due to space restrictions but I have enough room if I can intelligently snapshot individual changed files with the rest linked to the source not a copy.

Given all that, is there some other technique, feature or technology I'm really looking for?

I've long thought about versioning file systems. This is a killer feature and I've looked at Wayback, ext3cow, zfs, fuse solutions, or just cvs/svn/git overlays.

I consider ext3cow the model for my requirements. Transparent, efficient, but I can do without the extra ls abc@timestamp feature. As long as I somehow get automated, transparent versioning of my files.

It could be instantaneous or it could be based on snapshots on intervals of 10s, 30s, 1m, 5m, 15m, etc. Just something that will efficiently deal with thousands of files in a given directory all of various sizes, most small, but some upwards of 100m to 1gb.

ZFS isn't really an option as I'm on linux (and would prefer not to use it through fuse as I already have an ext3 setup I want to version, not something new).

What solutions are out there?