As @“Oliver.75” has stated it is not currently possible with the current architecture of the Plex Media Server (PMS) on the Shield. Please check the other discussions in this NVIDIA SHIELD category: “Will PMS ever allow Plex data on adopted storage?” and “Has anyone successfully relocated the Metadata folder with ROOT?”. Blueskies, Paul
That is an obsolete method that needs a rooted SHIELD. Plex now natively supports moving your database/metadata to external or adopted storage. This method shouldn’t be promoted anymore.
Plex metadata can already be stored on external drive in 6.3. I think this is more like an official acknowledgment from NVIDIA taking advantage of the release. You can check this thread for more info: