What Is a SQL Server File?

A SQL Server File represents a physical file provided by the operating system to store information for a SQL Server Database.

Every SQL Server Database uses 3 types of physical files:

1. Primary File - The primary data file contains the startup information for the database and points to the other files in the database. User data and objects can be stored in this file or in secondary data files. Every database has one primary data file. The recommended file name extension for primary data files is .mdf.

2. Secondary File - Secondary data files are optional, are user-defined, and store user data. Secondary files can be used to spread data across multiple disks by putting each file on a different disk drive. Additionally, if a database exceeds the maximum size for a single Windows file, you can use secondary data files so the database can continue to grow. The recommended file name extension for secondary data files is .ndf.

3. Transaction Log File - The transaction log files hold the log information that is used to recover the database. There must be at least one log file for each database. The recommended file name extension for transaction logs is .ldf.

A SQL Server Database must have one Physical defined as the Primary File, which contains the startup information for the database and points to the other files in the database.

SQL Server File information is stored in a system table called sys.database_files. Each record in this table represents a single SQL Server Physical File.

⇒ What Is sys.database_files?

⇐ SQL Server System Views and Functions

⇑ SQL Server System Views and Functions

⇑⇑ SQL Server Storage Tutorials