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I use rsnapshot for some years under Kubunt/Linux. But I am not sure how it (and underlying rsync) handles binary diffs: Image a large Thunderbird mailbox file or a 10 MB jpg photo and I change the EXIF data by adding a tag or a rating. What does rsnaphot do:

  • copy the new file (10 MB) completly or
  • only add the new EXIF data of new bytes?

If rsnapshot does not handle this binary diffs what tools do? rdiff-backup?

tardis
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  • From the man page: "The amount of space required is roughly the size of one full backup, plus a copy of each additional file that is changed." – Martin Schröder Jan 16 '16 at 13:09

1 Answers1

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It will copy the new file completely in the sense it will write a complete new file, but it can detect changes and only transmit these over the network.

Writing only diffs is not possible as traditional filesystems (e.g. extX) don't support these kind of diffs and every backup set is supposed to contain all files (mostly hardlinked in).

Sven
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  • The saved network bandwidth in not that importand as the "unnecessary" additional space needed on the backup harddisk. – tardis Jan 15 '16 at 09:42
  • That's not the assumption that `rsync` makes. For that, look into modern file systems like ZFS or btrfs. – Sven Jan 15 '16 at 09:44
  • Are there other tools that only save the diff? – tardis Jan 15 '16 at 09:46