SQL Server Error 5171 “MDF is Not a Primary Database File” – Problem Fixed

Written By Ashwani Tiwari
Anuraag Singh
Approved By Anuraag Singh
Published On March 18th, 2024
Reading Time 6 Minutes Reading

error 5171

At the time of using SQL Server, there are chances that you may come across a MDF is Not a Primary Database File or error 5171 SQL Server DB. SQL Server login failure issue or stick in a situation where you are not able to restore the Microsoft SQL Server database files. There could be another issue where you cannot create ‘tempdb’ database or unable to attach MDF file in your database. As we know these problems are associated with the SQL Server error 5171 that states:

“database.mdf is not a primary database file. (Microsoft SQL Server, Error: 5171)”

It is a very common issue that occurs during the corruption of SQL file. Because SQL database corruption can affect the MDF files and its performance. As a result, SQL Server encounters an error message that is shown below.

SQL Server Error 5171

Know About SQL Server Error 5171?

Whenever you get this error message “MDF is not a primary database file”, you should read the additional information that pops up with the error message. It helps you to understand the problem in a more clear way. It says:

It states when the SQL error 5171 occurs.

“ABC.mdf is not a primary database file. (Microsoft SQL Server, Error: 5171)”

This states the reason behind the SQL error. If the MDF file is corrupted, then SQL identifies it is an invalid file.

Why Does SQL Error Code 5171 Encounter?

Data stored in MDF file saves as pages and the size of each page is only 8 KB. The first page of the MDF file is known as the name of header page and contains crucial database information such as file signature, file size, compatibility, etc. and the actual data is stored in the rest of the pages. If either the header page or other page is not recognized by the SQL Server, then MDF file is not considered as a valid primary database file.

This situation becomes the cause of SQL database error 5171 in SQL Server 2008 / 2008 R2 / 2000 / 2005 / 2012 / 2014 / 2016 / 2017. Also, this problem in SQL Server can occur due to invalid registry entries, virus infections, power failure, damaged drivers, etc.

How to Fix SQL Error 5171 “MDF is Not a Primary Database File”?

In order to resolve the database .mdf is not a primary database file, first, you need to know the different scenarios. Because the process of SQL Server error 5171 fixing totally depends upon the situations you are in. Here, we will discuss two circumstances where SQL error 5171 occurs and different alternatives to solve this problem.

Case 1: The Database Corruption in Mirrored Databases

If you are running SQL Server on your system and you have some mirrored databases, then you need to set it online at the time of using one of the mirrored databases. To do so, you can run the following commands:


But, instead of setting the mirrored database, “Microsoft SQL error 5171” occurs. Hence, the solution is discussed here to help you.

Solution to Fix Error 5171 for Mirrored Databases

Step 1. At first, set principal database.

Step 2. Then, modify MDF file information by using “ALTER DATABASE MODIFY FILE” command.

Step 3. Now, stop the currently running SQL server instance by clicking on the Stop option.

SQL Server Error 5171

Step 4. After that, copy the MDF and LDF files to a different directory.

SQL Server Error 5171

Step 5. Finally, restart the SQL Server and attach  MDF and LDF files.

Case 2: Improper Upgradation of SQL Server

Another case, if you are using SQL Server 2014 and want to upgrade to the SQL Server 2016. And, after the completion of successful installation of new version, you try to attach the MDF file again and again. Then, it turns out to be MS SQL Server Error 5171.

Solution for Improper Upgradation of Server

This situation can be removed by running “sp_attach_db” command. It will help you to resolve the SQL error “MDF is not a primary database file”.

MDF is Not a Primary Database File

Fix SQL Server Error 5171 MDF is Not A Primary Data File Automatically

With the help of above mentioned resolution techniques, you can easily fix the error message “database.mdf is not a primary database file”. In case, if you are still facing the SQL error code 5171, then you need to opt a trouble-free professional SQL Recovery Tool from SysTools.

Because it is a very beneficial application that can repair the MDF file and fix this error message. This utility can also scan and restore all SQL data items like triggers, rules, functions, tables, stored procedures, etc. You can also download its free version from this link:-

Download Now Purchase Now

Now, below are the steps to use the automated solution & fix SQL error 5171 without any hassles.

Step-1. Launch the Automated Solution in the system.


Step-2. Hit the Open button to add MDF files here.

click Open button

Step-3. Select the Quick or Advanced Scan mode.

Select Scan Mode

Step-4. Set the Destination location to export data.

set destination

Step-5. Hit the Export button to fix error 5171 SQL Server.

export to finish


Here, it is discussed that the SQL database can be corrupted because of database mirroring and during the attachment of MDF file in an upgraded SQL Server. We also knew the situation where SQL Server error 5171 occurs and learned the solution to fix it.

Also, with the help of automated software, this error 5171 SQL Server can be resolved along with other errors. Because working with this utility is quite easy and it also saves a lot of time. Moreover, it comprises of several tools that makes the work of users easier.

Frequently Asked Questions:-

Q-1. Can I resolve error 5171 in SQL Server 2008 R2 with the tool?

Ans: If you are getting the error from the MDF file corruption, then tool will certainly fix it.

Q-2. I am getting “.mdf is not a primary database file. (microsoft sql server error 5171)” while attaching the database. How to fix this?

Ans: Try the methods written in this technical guide to resolve the error messages 5171 in Microsoft SQL Server.

Q-3. Is it possible to use the automated solution on any SQL Server version?

Ans: Yes, the utility easily fix the damaged MDF file of Microsoft SQL Server 2019 or all below editions.


By Ashwani Tiwari

Being a Chief Technical Analyst, I am aware of the technicalities faced by the user while working with multiple technologies. So, through my blogs and articles, I love to help all the users who face various challenges while dealing with technology.