> Forgive my shallow understanding of block chain, but wouldn't that make the archive immutable?
Kind of. The current state of the archive is mutable, but that changes to that state are logged to an append-only edit history — it's that edit history that is the "blockchain", and starting from a known good state and replaying all those edits must produce the current state. In fact, this is how cryptocurrencies work too — the state is the balances/utxo set, and the blockchain records transactions, which are effectively just mutations on that state.
In this situation, you'd look at the current state and find the deleted snapshot missing, but the edit log would have an entry saying the snapshot was added (and what its hash was at the time), then another entry saying it was deleted.
Kind of. The current state of the archive is mutable, but that changes to that state are logged to an append-only edit history — it's that edit history that is the "blockchain", and starting from a known good state and replaying all those edits must produce the current state. In fact, this is how cryptocurrencies work too — the state is the balances/utxo set, and the blockchain records transactions, which are effectively just mutations on that state.
In this situation, you'd look at the current state and find the deleted snapshot missing, but the edit log would have an entry saying the snapshot was added (and what its hash was at the time), then another entry saying it was deleted.