"Can only restore from ext/btrfs filesystems" / copied backup to another hdd

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The issue you are facing:
I am running nextcloudpi within a docker container. My external disk with the backup is corrupt and does not work properly, but I managed to copy the file nextcloud-bkp_20210528_1622204037.tar to another hdd. This hdd is formatted as gpt (I guess NTFS it is).

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. Run the ncp docker container.
  2. Start the restore function within the panel on :4443
  3. Get the error Can only restore from ext/btrfs filesystems

Correct ncp dos not support NTFS, it supports ext4/btrfs only

So should I copy the stuff to another hdd, which is formatted as btrfs?

Or can I somehow restore the stuff by copying the content of the backup file to specific directories? I cannot unzip it right now as my hdd is not large enough and I have no other linux pc running at the time.

Copying to another HDD which is formatted as btrfs did not work. It says that the .tar file is corrupt. I tried it also with other permissions, still failure. But it seems to me the file is ok, I can open the single files in it. I just do not know where to place the different files and directories.

Can I just copy the stuff in the .tar file to /var/lib/docker/volumes/ncdata/_data ?

What info is stores in the .bak file?