When using SQL Server, there are chances that you may come across an MDF is Not a Primary Database File or SQL Server Error 5171. SQL Server login failure issue or leave you stuck 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 the ‘tempdb’ database or are unable to attach the MDF file to your database. With the help of this write-up, we will learn more about this error and how it can be resolved in a quick and effortless way. Let’s begin by understanding the error first.
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Know More About SQL Server Error 5171
As we know, there are various problems associated with error 5171, which 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. SQL database corruption can affect the MDF files and their performance. As a result, SQL Server encounters an error message that is shown below.
Whenever you get this error message, “Error 5171: .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 clearer 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 SQL Server Error 5171 Arises? Common Causes Explained
Data in the MDF file is stored as pages, and the size of each page is only 8 KB. The first page of the MDF file is known as the 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 another page is not recognized by SQL Server, then the MDF file is not considered a valid primary database file. Here are some of the reasons that result in the occurrence of the error 5171 SQL Server – MDF is not a primary database file:
- MDF or LDF File Corruption
- Misplaced or Improperly Detached Database Files
- File Format Mismatch
- Failure During Backup or Restore Process
- Forced Shutdown or Server Crash
These situations can cause SQL error 5171 in SQL Server 2000 / 2005 / 2008 / 2008 R2 / 2012 / 2014 / 2016 / 2017 and in recent SQL Server versions such as 2019, 2022, and 2025. Also, this problem in SQL Server can occur due to invalid registry entries, virus infections, power failure, damaged drivers, etc.
When the error occurs, users encounter various issues and challenges with the SQL Server Error 5171 that further impact the user’s complete workflow. We will now take a look at these challenges and understand how they can be resolved using the appropriate solution.
Challenges Encountered Due to MDF is Not a Primary Database File Error 5171 SQL Server
- Inaccessibility of the Database – When the error occurs, the first issue encountered by the users is the inaccessibility of the database. After the error occurs, the database is directly impacted and further restricts users from accessing it.
- Disruptions and Downtime in Database – Another major impact of the error is the downtime of the database and the disruptions caused by SQL error 5171.
- Time-Taking Recovery Process – The process of repairing the error and accessing the database can be complex and time-consuming. Therefore, it is required for the users need to focus and choose the right method for SQL Server Error 5171.
- Database Incompatibility – Often, while transferring data from one SQL version to an older or different SQL version, users might encounter this error, resulting in compatibility issues.
- Compromised Data and File Integrity – With corruption in the LDF or MDF file, users might come across issues like compromised data in the database.
After learning the challenges, we will now take a look at the solutions that will help users to resolve the error. Let’s understand how these solutions can be helpful in such scenarios.
How to Fix SQL Error 5171 “MDF is Not a Primary Database File”?
In order to resolve the database error, first, you need to know the different scenarios. Because the process of fixing SQL Server error 5171 totally depends on the situations you are in. Here, we will discuss two circumstances where error 5171 occurs and different alternatives to solve this problem.
Case 1: 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 when using one of the mirrored databases. To do so, you can run the following commands:
ALTER DATABASE mydb SET ONLINE
But instead of setting the mirrored database, “Microsoft SQL Server 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 the principal database.
Step 2. Then, modify the MDF file information using the “ALTER DATABASE MODIFY FILE” command.
Step 3. Now, stop the currently running SQL Server instance by clicking on the Stop option to proceed with the MDF is not a primary database file repair.
Step 4. After that, copy the MDF and LDF files to a different directory to resolve SQL Server Error 5171.
Step 5. Finally, restart SQL Server and attach MDF file and LDF files.
Case 2: Improper Upgrade of SQL Server
Another case if you are using SQL Server 2014 and want to upgrade to SQL Server 2016. After the completion of successful installation of the new version, you try to attach the MDF file again and again. Then, it turns out to be error 5171 SQL Server.
Solution for Improper Upgrade of Server
This situation can be resolved by running the “sp_attach_db” command. It will help you to resolve the SQL error “MDF is not a primary database file”.
EXEC sp_attach_db
@dbname = N'mydb',
@filename1 = N'C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Data\mydb_Data.mdf',
@filename2 = N'C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Data\mydb_Log.ldf';
Fix SQL Server Error 5171 MDF is Not A Primary Data File Automatically
With the help of the above-mentioned resolution techniques, you can easily fix the error message “specified MDF file is not a primary database file”. If you are still facing the SQL error code 5171, then you need to choose a dedicated solution like SysTools SQL Recovery Tool.
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:-
Now, below are the steps to use the automated solution & fix SQL error 5171 without any hassles.
Step 1: Install the automated solution on the system. Next, browse for the MDF files for error repair.
Step 2: Click on the Open button to add MDF files here. Select the desired database file to fix the MDF is not a primary database file issue.
Step 3: Select the Quick or Advanced Scan mode to check for causes of SQL Server Error 5171. This will help detect any corruption in the database files.
Step 4: Set the Destination location to export data.
Step 5: Hit the Export button to fix error 5171 SQL Server.
Conclusion
Here, it is discussed that the SQL database can be corrupted because of database mirroring and during the attachment of an MDF file in an upgraded SQL Server. We also learned about the situation where SQL Server error 5171: MDF is not a primary database file 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 several tools that make the work of users easier.
Frequently Asked Questions:-
Ans: If you are getting the error due to MDF file corruption, then the tool will certainly fix it.
Ans: Try the methods written in this technical guide to resolve the error 5171 SQL Server in Microsoft SQL Server.
Ans: Yes, the utility can easily fix the damaged MDF file of Microsoft SQL Server 2025 and all lower editions.