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.
Database Files
SQL Server databases have three types of files, as following:
Database Files
SQL Server databases have three types of files, as following:
Primary
The
primary data file contains the start-up 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.
The recommended file name extension for primary data files is .mdf.
Secondary
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.
The recommended file name extension for secondary data files is .ndf.
Transaction Log
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.
The recommended file name extension for transaction logs is .ldf.
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