After @daftaupe convinced me to give #btrfs a try, I just learned how to mount multiple #subvolume|s of a #LUKS #encrypted devices through #pam_mount:
@daftaupe @martin
Seems that things change, but according to the FAQ, there are still some issues with this matter (know how much Space left and use it)
https://btrfs.wiki.kernel.org/index.php/FAQ#Why_is_free_space_so_complicated.3F
Il still think that mixing réplication (raid) and file system is a very bad idea.
@martin @hoper There's nothing magical :) it's basically having 2 btrfs partitionned drives, making a snapshot of a subvolume and sending that read-only snapshot from one to the other disk. That prevent us from the use a of a tool like rsync as there's an option to send only the increment when you already have subvolumes on the other drive. Based on : https://btrfs.wiki.kernel.org/index.php/Incremental_Backup