About Database Devices

After you install a SQL Server, you will need to create the database devices necessary to support the databases that will be created. When you create a database device, you provide both a logical and a physical name.

A logical name is a name used by SQL Server to identify the database device. The logical name follows the SQL Server rules for identifiers. For information about these rules, see the Microsoft SQL Server Transact-SQL Reference.
When using SQL Enterprise Manager (and Transact-SQL statements), you most often refer to the database device by its logical name.
A physical name is an operating-system filename that includes a full path and follows the rules for operating-system filenames.

These are examples of physical and logical names for database devices:



Type of file	Example logical name	Example physical name
Database device	CUSTOMER_LIST	C:\SQL60\DATA\CUST.DAT
Database device	RESERVATIONS	D:\DATA\RES_DATA.DAT
Database device	RES_TLOG	D:\TRANLOG\RES_TLOG.DAT

In most cases, at the time you create a database device for a database, you should also create a separate database device for its transaction log. It is important to store a database and its transaction log on separate devices so that you can dump the transaction log separately from the database and so that (if appropriate) you can mirror it. Putting the transaction log on a separate device also increases performance.

The minimum size for a device is 1 MB. Depending on the size of the database to be placed on a device, and depending on whether you plan to put more than one database on a device, you will probably want to make a new device bigger than 1 MB. For information on estimating the size of a database that you will place on a device, see Appendix B, Estimating Database Size.

A database device can be created only on a local disk drive. SQL Server does not support the use of database devices accessed over the network.