DragonFlyBSD: HAMMER has the ability to access file histories and undo deletions.
Is there a way to do this with HAMMER2? I've RTFM and looked on the mailing lists. I would ask there but it looks like that would be fruitless.
http://lists.dragonflybsd.org/pipermail/hammer/2017-October/001288.html
http://lists.dragonflybsd.org/pipermail/users/2018-November/357981.html
It seems like the data would still be there. http://lists.dragonflybsd.org/pipermail/users/2018-November/357981.html
>hammer2 does not actually delete a file when you rm or unlink it. Since recovery of the file is possible (this is the design of hammer2), there will still be an entry taking up data.