I have installed Nextcloudpi and it works perfectly. Got the app in the mobile phone and now my photos are stored in my server in an external HDD.
There is another external HDD used for backups.
Tried to do the nc-backup and got the following feedback and error:
Check free space…
Maintenance mode enabled
tar: /media/STORAGEB/nextcloud-bpk_20200829_1598709389.tar: Cannot write: Read-only file system
tar: Error is not recoverable: exiting now
error generationg backup
Maintenance mode disabled
Done. Press any key…