rsync and file renames

rsync doesn't handle file/folder renames well: if a folder containing lots of big files (a photos/videos library) is renamed in the source, then the existing files in the destination will be deleted, and all files will be copied again to the destination.

Unison appears to handle file renames, but what it actually does is detecting that the files already exist in the destination, and making a copy of them in the destination, from the destination. This saves bandwidth, but is still slow and will stress hard drives for no reason.

A tool made by one single person addresses this issue perfectly: rsync-sidekick

The author mentions that the tool doesn't make any changes, but to make sure of it, we can run it in a Docker container with readonly volumes. It will output a list of commands to rename and move stuff in the destination to reproduce the renames/moves made in the source.

Usage

• Build the container:

docker build -t rsync-sidekick .

• Run it:

docker run --rm \
	-v /<source-path>:/sync-src:ro \
	-v /<destination-path>:/sync-dst:ro \
	rsync-sidekick \
	/bin/bash -c "rsync-sidekick -shellscript /sync-src/ /sync-dst/ && echo && cat sync_actions_*.sh"

• Retrieve the output, check it visually, replace sync-src and sync-dst, and run it.

• Run rsync on dry-run:

rsync -ruvin /<source-path>/ /<destination-path>/

• Check the output; if all is ok, run rsync:

rsync -ruvi /<source-path>/ /<destination-path>/

Remote directories

rsync-sidekick only supports local directories at the moment, so to use it with a remote one, we need to mount the directory locally. Example with SSH:

mkdir ~/remote-dir
sshfs <server>:/<path-on-server> ~/remote-dir

Then you can use ~/remote-dir as a local directory.

To unmount it, run:

fusermount -u ~/remote-dir