Thank You for taking a time Kaizac.
I am sorry for a little confusion...it's because I didn't master or completely understand background mechanics of rclone nor mergefs.
I just learn by setting and watching results.
So this cache I was talking about...looks like it's this mergefs mount created with accessed folders structure for fast access. I don't care to much of it ( it's faking the system so the cloud files looks offline ) Originally I thought it was content and files downloaded by plex or RR's. Looks like my RR's through sabnzbd download properly to local folder in my data share and it's merged with online files provided by rclone in unionfs folder. LOVE IT.
I will check today but my unraid cache should be irrelevant....data folder will keep freshly downloaded files in unraid cache until mover will put them in array but it will work invisible on the share level so shouldn't affect merged unionfs etc.
I will set up this mergefs cache mount to keep it in cache all the time (backed to array only) so mover won't touch it and access should be very fast.
And finally I mentioned my 350TB library as in last 2 months Google shut down unlimited plan for cloud....Dropbox being only alternative is limiting/shutting it down as we speak....so I know (also from previous replies in this post) there is plenty of data hoarders like me with libraries between 100TB and 1PB for Plex purposes which are looking for a way out.
Yes only way is costly $8K-$10K minimum, investment in to drives, SAS cards and better servers.... My hybrid approach suppose to be "one disk at the time" solution for them when you can upgrade your unraid server gradually as you download data from Gdrive. I think google will give some time on notice before deleting all currently read-only accounts with hundreds TB's on them.
Thank you also for the script to copy folders. It won't work or at least will be hard to use by folder for me. I have only 6 of them.
Hopefully there is other option, maybe moving (not copying) data until for ex 20TB quota (when one disk added) so when executed again month later with another disk added, it will move next batch of files.
I manage directories and files in plex for years now...and splitting into many folders while managing it with RR's is pain in the ass.
Constantly changing root folders to match RR, Plex and genre ( kids, movies etc) doesn't work well with 15K+ movies and 3K+ TV shows.
To make things funnier I intend to encode some old stuff to H265, after having them locally...some of it RR's will redownload in this format, but as library of 4K HDR UHD movies with lossless quality is growing (every one is 60-80GB). I am looking towards higher total space needed.
Anyway this post derailed from main topic...I am sorry for that...but as reading past replies to learn I've seen lot of similar interest from others.