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Sorry to hear you’re facing problems 
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 20.0.5): 20.0.4.0
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04
Apache or nginx version (eg, Apache 2.4.25): 7.3.19
PHP version (eg, 7.4): 7.3.19
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:
- Run the ncp docker container.
- Start the restore function within the panel on :4443
- Get the error Can only restore from ext/btrfs filesystems