When I read this is thought it was a cool idea. I suspect it involves using ZFS’s file deduplication/copy-on-write mechanism to maintain a lightweight copy of a database on disk. Memory will still be required for holding the indexes etc, but in theory minimal extra disk space should be needed.

ZFS can also perform compression, which could be a big win as long as you have the spare cycles for lz4 (which is normally the case but may be an issue if you’re maxing out your NVMe disks’ bandwidth, say 3GiB/s+)