That is documented here https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/
“autoEmptyTrash”
I assume that the Drobo is using a Preferences.xml file to store the basic server prefs.
So you need to edit that file in an editor which is aware of UNIX-style line breaks (nowadays, even notepad.exe can do that) and either find and edit, or add that preference (if it’s not in there).
Keep in mind that due to the differences between the two systems, your move will not go without hickups.
- robocopy will very likely miss the symbolic links on the unix file system of the drobo. That means any manual poster selections you have made are very likely lost and will revert to the default poster upon the next metadata refresh. And that refresh will be necessary, because you may see no posters at all, initially.
- your media will be accessible under a different path on the new server. All media which was not matched to an external metadata source, can lose their metadata or may even be treated as newly added upon next library scan. The only solution to that would be a direct database file edit. [HowTo] Plex database modification - Moving media the right/wrong way - #10 by jelwell
- all items which were previously matched to a legacy/custom metadata agent may also encounter the same fate
