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so I'm looking at Oracle's docs https://docs.oracle.com/cd/E37670_01/E37355/html/ol_srbackup_btrfs.html https://docs.oracle.com/cd/E37670_01/E37355/html/ol_srb

so I'm looking at Oracle's docs https://docs.oracle.com/cd/E37670_01/E37355/html/ol_srbackup_btrfs.html https://docs.oracle.com/cd/E37670_01/E37355/html/ol_srbackup... while it doesn't allow you to delete a subvolume (i.e. what a snapshot is built off of), it does seem like one could conceptually just overwrite it via send/recieve? perhaps its a bit smarter and doesn't let snapshots be modified, but I'm now a bit unconvinced that it can be viewed as simply an "append only" interface.

ephbit 4y ago
> ... it does seem like one could conceptually just overwrite it via send/recieve? Don't think so. The man page for btrfs receive states: > btrfs receive will fail in the following cases: > 1. receiving subvolume already exists I also just tried it out. I created some subvol1-ro in a source filesystem, then sent it to the destination filesystem. Then deleted the source subvol1-ro. Then created a new subvol1-ro containing a different file and tried to send it to the same destination. Result: > ERROR: creating subvolume subvol1-ro failed: File exists
- compsciphd 4y ago
  so, if I use a subvolume (not as a snapshot, but as something I can modify) I can't use send/receive on it? it seems a little weird. I'd assume I should be able to send modifications to the remote end (and my argument is, if one can send modifications, one should be able to send modifications that effectively delete all content). I temper this argument that even if true, perhaps subvolumes marked as snapshots one cannot do this to.
  - ephbit 4y ago
    AFAIK only read only snapshots can be sent and received. It kind of makes sense, since a writable snapshot could be written to during the send/receive so that the remote result would not match any clearly defined local state. A received ro snapshot can be used as a base for a new writable snapshot.

ephbit 4y ago

> ... it does seem like one could conceptually just overwrite it via send/recieve? Don't think so. The man page for btrfs receive states: > btrfs receive will fail in the following cases: > 1. receiving subvolume already exists I also just tried it out. I created some subvol1-ro in a source filesystem, then sent it to the destination filesystem. Then deleted the source subvol1-ro. Then created a new subvol1-ro containing a different file and tried to send it to the same destination. Result: > ERROR: creating subvolume subvol1-ro failed: File exists

compsciphd 4y ago
so, if I use a subvolume (not as a snapshot, but as something I can modify) I can't use send/receive on it? it seems a little weird. I'd assume I should be able to send modifications to the remote end (and my argument is, if one can send modifications, one should be able to send modifications that effectively delete all content). I temper this argument that even if true, perhaps subvolumes marked as snapshots one cannot do this to.
- ephbit 4y ago
  AFAIK only read only snapshots can be sent and received. It kind of makes sense, since a writable snapshot could be written to during the send/receive so that the remote result would not match any clearly defined local state. A received ro snapshot can be used as a base for a new writable snapshot.