Logical Volume Manager let you handle a number of partitions and also to resize them. It's also nice for backups because you can take a snapshot of the file system during the backup process runs.
If it is only about the total file size or number of files, you can use system quotas.
It is just about total file size. A system quota would be good.
I'm not exactly getting your meaning though: Operating system quotas, or ownCloud system quotas? If ownCloud has a system quota I can't seem to find it.