A Microsoft file hosting and synchronization service.
I believe the max file size is 20GB.
Do you get any error messages at onedrive.live.com? Does OneDrive always just say something like "processing changes" with no list of the files currently being processed? If so I find that it's one or two files that can't be synced and that causes the whole process to bog down. It could be a name conflict between two files. So if you could possibly locate these files and remove them or rename them then that might help.