Fantasy hard drive (or array) ...
... 3 position physical (key?) switch on drive (or array)
(1) looks to the BIOS/OS like a normal drive (or array) but keeps, inaccessibly and invisibly, all previous versions of files; perhaps also ignores destructive operations such as partitioning and formatting
(2) all versions above become visible but drive is read-only
(3) disk accessible as normal for partitioning, formatting or just maintenance (e.g. deleting of old versions of files).
I'm not sure that my drive usage is typical but it seems to me that ordinary file store disk usage would not be greatly increased by keeping all previous versions of files - by far the biggest chunk of my diskspace is taken up by files that are their initial version.
Even if this were not practical for operational disks or arrays, surely it's achievable for disk-based back-up solutions?