Is Docker duplicating data?

My forum is hitting the limits of its server’s file system, but before upgrading the server I wanted to check there isn’t any config that would make it use the FS more efficiently.

I have a standard install in /var/discourse, which is 20GB. But the /var/lib/docker folder is 21GB, most of which seems to be in “overlays” for the FS.

I don’t understand how Docker works at the FS level, and I assume it’s not just carelessly duplicating data, but the two folders being so similar in size does make me wonder if there’s a chance the /var/discourse data has been copied into the Docker folder.

Have you done

./launcher cleanup

It’s likely extra docker containers (so the answer to your question is yes)


I did run docker container prune, which didn’t do anything. The container list only shows the main app and the mail receiver. I also ran docker image prune which freed 1.5GB space.

I didn’t think of running the launcher’s cleanup. Will try and report back.

launcher cleanup cleaned up 6.6GB of images (I’m not sure why docker image prune didn’t remove them!), and also removed a 3.4GB Postgresql ‘backup data cluster’. So that will give us enough space for a while.


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