All,
The now rather lengthy (lengthy is good) discussion regarding Tails persistence backup has not considered the benefits of an alternative persistence file system, one designed with fast, easy backups in mind. Of the several such file systems that come to mind, btrfs is perhaps the easiest to implement. Recent Linux kernels support btrfs fully, and most distros come with btrfs tools installed.
If the Tails persistence volume were a btrfs file system, any backup application could be employed to copy data there. The btrfs "snapshot" feature would then make what are in effect incremental backups simple and fast. These snapshots require very little additional storage space, and rather than being something special to the btrfs file system, snapshots are basically subvolumes which can be browsed and/or mounted. Importantly, any backup application running on any other Linux file system can move data into and out of a btrfs file system. No walls, no fences, and no special backup file formats required (though optional).
The btrfs wiki at kernel.org documents just about everything there is know about btrfs:
https://btrfs.wiki.kernel.org/index.php/Main_Page
regards,
alienpup
