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by nextaccountic
1130 days ago
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What I don't understand is: aren't zfs snapshots writable, like in btrfs? If I wanted to rollback the live filesystem into a previous snapshot, why couldn't I just start writing into the snapshot instead? (Or create another snapshot that is a clone of the old one, and write into it) |
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ZFS snapshots, following the historic meaning of "snapshot", are read-only. ZFS supports cloning of a read-only snapshot to a writable volume/file system.
* https://openzfs.github.io/openzfs-docs/man/8/zfs-clone.8.htm...
Btrfs is actually the one 'corrupting' the already-accepted nomenclature of snapshots meaning a read-only copy of the data.
I would assume the etymology of the file system concept of a "snapshot" derives from photography, where something is frozen at a particular moment of time:
> In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. […] To avoid downtime, high-availability systems may instead perform the backup on a snapshot—a read-only copy of the data set frozen at a point in time—and allow applications to continue writing to their data. Most snapshot implementations are efficient and can create snapshots in O(1).
* https://en.wikipedia.org/wiki/Snapshot_(computer_storage)
* https://en.wikipedia.org/wiki/Snapshot_(photography)