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Know What are Files and Filegroups in SQL Server

Published By Nilesh Kumar
Debasish Pramanik
Approved By Debasish Pramanik
Published On January 25th, 2024
Reading Time 5 Minutes Reading
Category SQL Server

SQL Server comprises of two sorts of files Log files and Data files; these can additionally be gathered into Filegroups with the end goal of allocation and administration. Data files justifiably comprise of data and objects like tables, indexes, views, and so forth. Log files then again track all transactions and furthermore store data that would be expected to restore transactions in databases. Along these lines, in this blog, we will talk about what are files and filegroups in SQL server.

Important Note: In case if your database MDF / NDF files are corrupted then try Enterprise-Grade Level Professional Software to recover database items.

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Database Files

  1. Primary data files: This incorporates the startup data for the given database and furthermore signifies different files of the database. This can be used for putting away data and objects, secondary data files can likewise be used for this reason. There is just a single primary data file in all databases, with filename augmentation .MDF.
  2. Secondary data files: These are used for storing data and are user-defined and discretionary. This additionally helps in spreading data on various disks by using an alternate disk for storing each file. It permits a database to develop in any event, when it fills the most extreme size took into account a solitary Windows file. Its filename expansion is .NDF.
  3. Transaction Log: This stores the data required for database recovery and furthermore gives notices if there should be an occurrence of any alteration. Each database must have one log file. Its filename expansion is .LDF.

File Size

SQL Server files can develop consequently from their initially determined size. At the point when you characterize a file, you can determine a particular growth increment. Each time the file is filled, it expands its size by the growth increment. If there are numerous files in a filegroup, they won’t autogrow until all the files are full.

Each file can likewise have a most extreme size determined. In the event that a greatest size isn’t indicated, the file can keep on growth until it has used all accessible space on the disk. This component is particularly helpful when SQL Server is used as a database installed in an application where the client doesn’t have advantageous access to a system administrator. The client can let the files autogrow as required to diminish the authoritative burden of checking free space in the database and manually assigning extra space.


  1. The filegroup contains the primary data file and any secondary files that aren’t placed into different filegroups.
  2. User-defined filegroups can be made to gather data files together for authoritative, data allocation, and position purposes.

For example: file1.ndf, file2.ndf, and file3.ndf can be made on three disk drives, separately, and assigned to the filegroup fgroup1. A table would be created explicitly on the filegroup fgroup1. Queries for data from the table will be spread over the three disks; it will improve execution. A similar performance improvement can be practiced by using a solitary file made on a RAID (Redundant Array of Independent Disk) stripe set. Be that as it may, files and filegroups let you effectively add new files to new disks.

Default Filegroup

All the made objects, which have not been allocated any of the current filegroups, will turn into a part of the default filegroup. Whenever, there is one filegroup which will be assigned the default filegroup. The default filegroup must be sufficiently large to oblige every one of those objects which are not a part of any filegroup. The Primary filegroup will remain default filegroup except if adjusted by using the ‘ALTER Database’ command.

Rules for Making Files and Filegroups

The accompanying principles relate to files and filegroups:

  1. A file or filegroup can’t be used by more than one database. For example, file sales.MDF and sales.NDF, which contains data and objects from the business database, can’t be used by some other database.
  2. A file can be an individual from only one filegroup.
  3. Transaction log files are never part of any filegroups.

How to Secure Data Stored in SQL Server Database?

So far we have discussed What are Files and Filegroups in SQL Server In circumstances like a database crash, it turns out to be intensely critical to recovering the data stored in the SQL Server database. While your standard recovery procedures would have the option to bring back a decent measure of data, particularly the ones stored since the last backup can be in danger. To recover such data, you can use Emaildoctor Recover SQL Database Software. This amazing tool is intended to bring back each and every bit of the file stored in the database fit as a fiddle. Also, the application can be used to restore coincidentally deleted SQL database objects as well.

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Also Read: Read this to Recover deleted objects of SQL Server.

Likewise, most databases will function admirably with a solitary data file and a solitary transaction log file. On the off chance that you use different data files, make a second filegroup for the extra file and make that filegroup the default filegroup. Along these lines, the primary file will contain just framework tables and objects. So, in this blog, we have talked about what are files and filegroups in SQL Server. Moreover, to recover the corrupt database files, we recommend using expert Solution.


By Nilesh Kumar

As a Chief Technical Writer, I know the technical issues faced by home and professional users. So, I decided to share all my knowledge via this blog. I love to help you with challenges while dealing with technical jargon.