borgbackup developer here:

TL;DR: don't panic, all is good. :-)

Longer version:

- borg 1.x style “append-only” was removed, because it heavily depended on how the 1.x storage worked (it was a transactional log, always only appending PUT/DEL/COMMIT entries to segment files - except when compacting segments [then it also deleted segment files after appending their non-deleted entries to new segments])

- borg 2 storage (based on borgstore) does not work like that anymore (for good reasons), there is no “appending”. thus “—append-only” would be a misnomer.

- master branch (future borg 2 beta) has “borg serve —permissions=…” (and BORG_PERMISSIONS env var) so one can restrict permissions: “all”, “no-delete”, “write-only”, “read-only” offer more functionality than “append only” ever had. “no-delete” disallows data deleting as well as data overwriting.

- restricting permissions in a store on a server requires server/store side enforced permission control. “borg serve” implements that (using the borgstore posixfs backend), but it could be also implemented by configuring a different kind of store accordingly (like some cloud storage). it’s hard to test that with all sorts of cloud storage providers though, so implementing it in the much easier to automatically test posixfs was also a motivation to add the permissions code.

Links:

- docs: https://github.com/borgbackup/borg/pull/8906/files

- code: https://github.com/borgbackup/borg/pull/8893/files

- code: https://github.com/borgbackup/borg/pull/8844/files

- code: https://github.com/borgbackup/borg/pull/8837/files

Please upvote, so people don't get confused.