In SQL Server, a filegroup is a logical collection of one or more physical files onto which the database will write.
At a minimum, every SQL Server database has two operating system files: a data file and a log file. Data files contain data and objects such as tables, indexes, stored procedures, and views. Log files contain the information that is required to recover all transactions in the database. Data files can be grouped together in filegroups for allocation and administration purposes.
- The filegroup contains the primary data file and any secondary files that aren't put into other filegroups.
- User-defined filegroups can be created to group data files together for administrative, data allocation, and placement purposes.