Thanks this clarify a lot of things for me. This makes sense that I need higher buffer-size because my internet pipe is sometimes not good when I saturate it with torrent and ‘rclone move’
I’m using Intel Celeron j1900 with barely enough passmark and only 4GB RAM serving around 55TB in rclone.
Yep. I did the normal max free memory / max expected # of concurrent streams to get my buffer size.
Won’t you get into trouble when Plex is scanning and analyzing new media?
If you had the buffer-size too high, you’d most likely run out of memory on a new plex scan of media as it would open quite the # of files. Better to start small if you haven’t analyzed your plex library and bump it up after.
Is it know what the max open files can be when Plex does a scan? I’ve read in some of your other post around 35 at a time?
A small buffer of say 32mb is that useful or better stick with 0 as a general value?
I don’t think there is a limit as plex does what plex does 
I’ve monitored full scans and the most I’ve seen open personally is 35.
If you are scanning a whole new library, I’d keep it small (0-32MB) and base that on your memory of your system as to what the top value can be.