I can now confirm the SQL edit process really is as easy as I expected.
I first tried the ‘official’ Plex method of copying all the media to the new location, but since it was totally impractical to find space to duplicate 5 TB (storage location not changing, just need to change a folder name) I just made a symlink and Plex would see that as a copy at the new path. Apart from that, it’s dreadfully slow and each library would take an unacceptably long time to re-scan and add the new folder. With half a dozen libraries to update (just to change the name of the storage folder) and one could take nearly an hour, then when I saw that in many cases PMS had NOT matched every item. So some entries were not showing that ‘2’ flag on the icon. Some were simply displayed twice and not matched up. I gave up. Not only was this official method way too slow to be of any real use (for what is after all a VERY simple change), but it was also screwing up.
So I grabbed DB Browser and had a go at editing the paths in the SQLite database. I tried a few edits, but then it crashed. When I opened it all up again, the edits had not been saved. I then noticed there is an extra button to click in order to actually save the changes (unusual when dealing with SQL). So I made the same 2 edits and saved the changes. Then it crashed. Only one of the edits had actually been saved.
I tried saving and closing the database after each edit, but mostly it crashed before I had the chance. So in the end I gave up with that.
I then used SQLPro for SQLite, which I have previously used successfully with SQL databases. This has no extra ‘Commit’ step, but it worked perfectly and never crashed so in a short time I had everything updated to the new paths as I require.
Re-started Plex and everything is correct and all content accessible at the new locations (just new names, not actually moved at all).
So if I ever need to do it again, I wouldn’t waste my time on the official method and instead go straight to using a good SQLite editor and directly update the database. Works perfectly. How can it not. I would add however that if you’re not comfortable editing SQL databases, this method is probably not for you. Which rather suggests…
Plex really should incorporate this as part of PMS. It’s not complicated and after typing in the new paths (the interface for this would need thought) the actual database changes take seconds - literally.
There would need to be some care taken, like e.g. the new paths MUST already exist with the data in place and the database would need to be locked from other Plex usage and then re-read, like stopping and re-starting Plex. However, this is easy for the actual Plex devs as they can make Plex do whatever they need.
Now Plex is configured with the correct paths, I’m moving everything to the actual new media server. Make no mistake, it takes a LONG time to transfer 5 TB from one server to another, even on a local Gigabit network. Ho hum…