https://support.plex.tv/hc/en-us/articles/200289306-Updating-vs-Refreshing-a-Library
Update my library automatically
Typically, the most desirable way to keep your Libraries updated is using the Update my library automatically feature. This uses capabilities of the operating system to detect when content has changed and then initiate a Library update.
Note: In most cases, this should work for content on local filesystems. It will generally not work for network shares mounted via SMB, NFS, AFP, or similar.
If you have this option enabled and Library updates don’t happen automatically (you should wait 60 seconds after all activity on the drive finishes), automatic updates may not be supported on your operating system/filesystem and you may wish to use periodic updates instead.
