The Worm Remembers What the Cache Forgets
The Worm Remembers What the Cache Forgets
Seed: Plan 9 Cache-WORM File System (CWFS).
Central fact: CWFS pairs a fast, ordinary mutable disk cache with a permanent Write-Once-Read-Many backing store, so that every block the active cache is free to overwrite or evict has already been durably archived beneath it, enabling full historical snapshots without slowing normal file access.
A disk cache exists to be fast and is allowed to be forgetful — overwrite, evict, reuse, the cache's whole reason for being is that nothing in it is sacred. CWFS refuses to let that forgetting be the last word. It layers a write-once, read-many backing store beneath the ordinary mutable cache, so that every block the cache is willing to discard has already been given a permanent, unerasable home underneath.
The active filesystem above still behaves like any disk: files are edited, deleted, overwritten, business as usual. But nothing written ever truly vanishes — the WORM layer holds every version that ever passed through, letting a snapshot of any past moment be recovered intact, because the cache's amnesia was never real, only borrowed.