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Find where some files are stored docker synology nas

Allthough I have some containers running I do not understand everything (read : a very little) of docker.
I have Home Assistant running in docker.An automation stores files to a folder. However I cannot find this folder so I assume it is stored somewhere I don’t have access to in the “normal” synology file manager.

With putty I found a directory called /volume1/@docker/btrfs#/subvolumes and after that a lot of subfolders with very, very long names:
I suppose those subfolders where created when I created a container.
When I use portainer, and I go to the container that created the files with home assistant, a long id is shown, but it seems it is not the name of the subfolder (subvolume) ? cd “longstring” gives an error.

So I have two questions :

  1. How can I tell what subvolume belongs to what container
  2. Because I expect that a lot of those subvolumes are not necessary anymore, can I delete them with rmdir “longstring” , and how can I tell what subvolume belongs to what container? I assume every subvolume takes some diskspace.

Forgive me my poor english
Thanks in advancd

How did you create your containers?
Using the Synology-UI? Check the volume tab of your container details. If you don’t map a host folder (=must be a folder withing a shared folder) to a container folder, all data is written into the container filesystem.

The host folder you mapped is the place where you’d expect the permanent data to be stored.