Duncan, thank you for this comprehensive post. Really helpful as always! [...]
> As for restoring, since a snapshot is a copy of the filesystem as it > existed at that point, and the method btrfs exposes for accessing them is > to mount that specific snapshot, to restore an individual file from a > snapshot, you simply mount the snapshot you want somewhere and copy the > file as it existed in that snapshot over top of your current version > (which will have presumably already been mounted elsewhere, before you > mounted the snapshot to retrieve the file from), then unmount the > snapshot and go about your day. =:^) Please, how do I list mounted snapshots only? [...] > > Since a snapshot is an image of the filesystem as it was at that > particular point in time, and btrfs by nature copies blocks elsewhere > when they are modified, all (well, not "all" as there's metadata like > file owner, permissions and group, too, but that's handled the same way) > the snapshot does is map what blocks composed each file at the time the > snapshot was taken. Is it correct, that e.g. ownership is recorded separately from the data itself, so if I would change the owner of all my files, the respective snapshot would only store the old owner information? [...] > > The first time you do this, there's no existing copy at the other end, so > btrfs send sends a full copy and btrfs receive writes it out. After > that, the receive side has a snapshot identical to the one created on the > send side and further btrfs send/receives to the same set simply > duplicate the differences between the reference and the new snapshot from > the send end to the receive end. As with local snapshots, old ones can > be deleted on both the send and receive ends, as long as at least one > common reference snapshot is maintained on both ends, so diffs taken > against the send side reference can be applied to an appropriately > identical receive side reference, thereby updating the receive side to > match the new read-only snapshot on the send side. Is the receiving side a complete file system in its own right? If so, I only need to maintain one common reference in order to apply the received snapshot, right. If I would in any way get the send and receive side out of sync, such that they do not share a common reference any more, only the send/receive would fail, but I still would have the complete filesystem on the receiving side, and could copy it all over (cp, rscync) to the send side in case of a disaster on the send side. Is this correct? Thank you! Best, Wolfgang -- Wolfgang Mader wolfgang.ma...@fdm.uni-freiburg.de Telefon: +49 (761) 203-7710 Institute of Physics Hermann-Herder Str. 3, 79104 Freiburg, Germany Office: 207 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
