[SQL Server] Restore a filegroup

If you have a very large database and only a single file is damaged, there is no need to restore the entire database. The thing you gain by separating your database into a number of files of filegroups allows you to reduce your RTO because there is less data to restore in the case of a single file or filegroup being damaged.

All editions of SQL Server support offline file restore. SQL Server Enterprise Edition supports online file restore. With online file restore only the restoring file group is unavailable until it is restored and recovered.

see also : [SQL Server] Perform page recovery