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SQL Server uses MDF for data files and LDF for log files, but what are NDF files?

Whats the benefits of these files?

+1  A: 

From Files and Filegroups Architecture

Secondary data files

Secondary data files make up all the data files, other than the primary data file. Some databases may not have any secondary data files, while others have several secondary data files. The recommended file name extension for secondary data files is .ndf.

Also from file extension NDF - Microsoft SQL Server secondary data file

See Understanding Files and Filegroups

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.

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For example, three files, Data1.ndf, Data2.ndf, and Data3.ndf, can be created on three disk drives, respectively, and assigned to the filegroup fgroup1. A table can then be created specifically on the filegroup fgroup1. Queries for data from the table will be spread across the three disks; this will improve performance. The same performance improvement can be accomplished by using a single file created on a RAID (redundant array of independent disks) stripe set. However, files and filegroups let you easily add new files to new disks.

astander
@Astander - Whose responsible to create or manage create process of these NDF files - DBA or developers or ... ? what should adeveloper know about these files ? justhe/she should be aware ofthese ind of files or should be able to create and manage these files ?
Nasser Hadjloo
@Nasser: It will most probably fall under the DBA's responsibility.
Daniel Vassallo
+1  A: 

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.

Source: MSDN: Understanding Files and Filegroups

The recommended file name extension for secondary data files is .ndf, but this is not enforced.

Daniel Vassallo
@daniel - How to use it?
Nasser Hadjloo
@Nasser: You may want to check out the following article: http://msdn.microsoft.com/en-us/library/aa174545(SQL.80).aspx. See the example at the bottom.
Daniel Vassallo