Most likely because ownCloud don’t have the permissions to write / delete from the NFS mount. This FAQ has some pointers how to check permissions and so on:
Problem
You’re getting one of the following error message:
Can’t create or write into the data directory
Can’t write into config directory!
Data directory (/mnt/data) is invalid (/mnt/data is an example here)
Solutions
The messages basically means that ownCloud can’t access and write into the mentioned directories (as the messages are telling). There are a few issues which are showing up quite often:
Missing permissions
You have permission issues that the users which is running your webse…