AlexT,
just want to clarify something with you in regards to your uppermost post:

"There is no such limit on filesystem (about 2K file) ! the most close limit is about 30K subfolders(not files), but Dolphin do not use subfolders in such cases!"

maybe its just a misunderstanding, but you mention the filesystem limitation and you state that dolphin do not use subfolders in such cases. was this referring to the migration itself or overall in general?