Why we need secondary data files in SQL server?

Why we need secondary datafiles in the database? What are thier advantages? Also why we need multiple secondary files?
asqldbaAsked:
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Tapan PattanaikConnect With a Mentor Senior EngineerCommented:

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.

For more details check this below link:

http://msdn.microsoft.com/en-us/library/ms179316.aspx
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Tapan PattanaikSenior EngineerCommented:

hi asqldba,
                 Check these links ,
             

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.

For more details check this below link:

http://msdn.microsoft.com/en-us/library/ms179316.aspx

http://www.dotnetspider.com/resources/19525-Database-Files-SQL-Server.aspx
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asqldbaAuthor Commented:
I do understand that there are 3 type of file: Primary, Secondary and Log. My question is why we need secondary data files? Why can't we just keep just two? MDF and LDFs are needed but why we need NDF?
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Tapan PattanaikSenior EngineerCommented:
hi asqldba,

The big question now is why do we need secondary database files when I can store data in primary database files?

Well this has certain advantages and disadvantages. The main disadvantage of multiple database files is administration. You need to remember these different files, their locations, and their use. The main advantage is that you can place these files on separate physical hard disks, avoiding the creation of hot spots and thereby improving performance. When you use database files, you can back up individual database files rather than the whole database in one session.
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Jerryuk007Connect With a Mentor Commented:
The main reason I see as having multiple data files is so you can split a large database across multiple drives, or separate indexes, etc... for better performance. Or backup the database in "steps" (as mentioned above)

On small to average size database, I would generally use just one data file and one log file (there are of course a few exceptions...)

Jerry
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