This question already has an answer here:
I've got a database with 3 Filegroups and each filegroups own a single file, Filegroup names are Primary, SecondFG and ThirdFG. I want to backup ThirdFG separately each time without backing up the others. I've tried it in many ways but when I want to restore database filegroup backup I get the error for other Filegroups or files are not included in the backup file! but When I backup all FileGroups together there would be no problem, please guide me how to backup and restore single filegroup, by the way I've read all BOL and I couldn't solve my problem!