Wonder how this compares to Venti[1]. It looks a lot more complicated (not really a good thing).

[1]: https://doc.cat-v.org/plan_9/4th_edition/papers/venti/

You could use tape as a backing for Venti arenas; don't know if anyone ever did so. The original Bell Labs fileserver used an MO jukebox for WORM archives, which today LTFS tape is a pretty close approximation of.