Nextcloudpi on docker: cant run container with external storage

Recently I installed nextcloudpi in docker with

sudo docker run -d -p 4443:4443 -p 443:443 -p 80:80 -v /home/user/storage/nextcloud:/data --name nextcloudpi ownyourbits/nextcloudpi-armhf <ip-adress-of-pi>

the folder /home/user/storage is a mounted external storage (following this tutorial https://www.techjunkie.com/build-nas-raspberry-pi-linux/)

Running the container gives me the following output:

Running nc-init
Setting up a clean Nextcloud instance... wait until message 'NC init done'
Setting up database...
Setting up Nextcloud...
Console has to be executed with the user that owns the file config/config.php
Current user: www-data
Owner of config.php: root
Try adding 'sudo -u root ' to the beginning of the command (without the single quotes)
If running with 'docker exec' try adding the option '-u root' to the docker command (without the single quotes)

I tried

sudo docker run -d -p 4443:4443 -p 443:443 -p 80:80 -v /home/user:/data --name nextcloudpi ownyourbits/nextcloudpi-armhf <ip-adress-of-pi>

and everythink workes well as far as I can tell. I can load the nextcloudpi config UI as well as the nextcloud GUI.

I have tried some chown and chmod for the /home/user/storage folder, without any succes.

How can i use the external storage as directory of the nextcloud? Running it on a SD card sounds wrong to me.

You need to chown -R that directory to the right UID (to discover it, run docker exec {all the stuff} id) (it should be 33)

What caused my trouble was the fomat type of my external hdd, which was set to ntfs. As soon as I used FAT it worked well with chown -R.