EDIT: i realized i answered about btsync while question was about syncthing, sorry. Regarding detecting file modifications: my friend had issues with his synol

EDIT: i realized i answered about btsync while question was about syncthing, sorry. Regarding detecting file modifications: my friend had issues with his synology diskstation eating 100% cpu with btsync with around 50k files. With less files it was down to 20%. We never debugged it properly but it may be polling issues, but it could also have been out of ram-swapping issues (512MB ram was not enough). Others have reported issues with many files: https://forum.bittorrent.com/topic/23802-syncing-600gb-10-million-files-recommend-settings/ https://forum.bittorrent.com/topic/23802-syncing-600gb-10-mi...