Microsoft® SQL Server 2012 Unleashed

Data Storage in SQL Server

A database is a storage structure for database objects. It is made up of at least two files. One file, referred to as a data file, stores the database objects, such as tables and indexes. The second file, referred to as the transaction log file, records changes to the data. A data file or log file can belong to only one database.

SQL Server stores data on the data file in 8KB blocks, known as pages. A page is the smallest unit of input/output (I/O) that SQL Server uses to transfer data to and from disk. An 8KB page is equal to 1024 bytes σ 8, or 8192 bytes. There is some overhead associated with each data page, so the maximum number of bytes of data that can be stored on a page is 8060 bytes. The overhead on a data ...