This got disabled by purpose for security reasons. It allows an ownCloud Admin to take over the system without the system administrator. You can enable it via config.php:
master ← 26653
opened 07:56PM - 06 Apr 17 UTC
Fixes #26653
## Description
Option to mount a new local storage remov… ed unless ```files_external_allow_create_new_local``` variable specifically set to ```true``` in config.php
## Related Issue
https://github.com/owncloud/core/issues/26653
## How Has This Been Tested?
Included the ```files_external_allow_create_new_local``` option and set to ```true``` and ```false```, works as desired
## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)
## Checklist:
- [x] My code follows the code style of this project.
- [x] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [x] I have read the **CONTRIBUTING** document.
- [ ] I have added tests to cover my changes.
- [x] All new and existing tests passed.
@PVince81