in order to increase my storage-capacities on my nextcloud I added an additional virtual hdd (my nextcloud runs on proxmox) and mounted it on /var/snap/nextloud/common/nextcloud/data/hdd (ext4).
I also tried adding it while beeing mounted on media/hdd or mnt/hdd but both didn’t seem to work.
So this setup worked really well until I noticed, that the data I put on that hdd got also stored on the dev/vda2 disk.
With df -h I could indeed confirm that the data got stored twice and I have really no idea why. This is also a problem because the boot ssd of the vm is only 32GB big and I plan on storing a few TB.
I also did not find any forum post that spoke of this kind of problem.
I haven’t used proxmox or snap to install it before, however, your problem looks like a weird situation about mounting disks on Linux. ext formatted disks can only be mounted for a single user. You can overcome the situation as I did before.
I suggest before mounting if there is the directory /var/snap/nextcloud/data/hdd delete it, then recreate it.
Before mounting change the owner of the directory to web user (www-data, wwwrun, www, etc). chown -R user:group /path/to/dir/
Mount disk
Change the owner (chown -R) -to www-data, wwwrun, www, etc- and the mod (chmod -R) -to 750- of the directory and all files and directories in it.