Backup/Restore File Groups SQL Server
You can back up individual files and filegroups only when your database is using the full or bulk_logged recovery model, because you must apply log backups after you restore a file or filegroup; you can't make log backups of a database that's using the simple model.
Unlike full database and differential backups, a backup of a file or filegroup doesn't back up any portion of the transaction log. So, none of the transaction log is in a file or filegroup restore, and you still need to restore the log.
You can restore individual file or filegroup backups from a full database backup.
Immediately before restoring an individual file or filegroup, you must back up the transaction log. You must have an unbroken chain of log backups from the time the file or filegroup backup was made until the time the files or filegroups are restored.
After restoring a file or filegroup backup, you must restore all the transaction logs made between the time you backed up the file or filegroup and the time you restored it. Restoring these interim transaction logs guarantees that the restored files are synchronized with the rest of the database.