SQL Error 5171: MDF Is Not A Primary Database File

If this error message: MDF is not a primary database file pops up while opening or attaching an SQL Server database file, don't worry. EaseUS SQL Recovery with reliable methods will be available here to help you resolve this issue, repairing MDF to work again. Read on and fix SQL error 5171 in two effective ways.

Updated by Daisy on Jul 20, 2023
Written by Tracy King
 | Home > MS SQL Database Recovery

Applies to: 5171 error in MS SQL Server 2017, 2016, 2014, 2012, 2008, etc.

Workable Solutions Step-by-step Troubleshooting
1. Repair with SQL Repair Tool

Step 1. Stop MS SQL Server service

Step 2. Run EaseUS SQL repair tool

Step 3. Choose the database objects...Full steps

2. Manually Resolve SQL Error

Step 1. Run Microsoft SQL Server Management Studio

Step 2. Modify MDF file information with ALTER DATABASE MODIFY FILE command...Full steps

SQL Server Error 5171: MDF Is Not A Primary Database File

If you receive this error message, it means that you are having Database error 5171 on SQL Server:

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

SQL Server error 5171.

Error 5171 is a common issue that many SQL Server administrators have met when they try to log in to SQL or restore the MS SQL database. This error may also happen when you can't create 'tempdb' database or can't attach an MDF file to the database.

To resolve this error, you should check the causes first so to figure out the right solution:

  • MDF files corrupted or not recognized
  • Invalid registry entries
  • Virus infection
  • Power failure
  • Drivers damaged

If the 5171 error is caused by the latter four reasons, you are highly suggested to modify the registry entries, clean up the virus and restart SQL, check the power connection, and update drivers. If the problem exists in the MDF database file, read on to find two solutions here, to get rid of this issue. 

Solution 1. Repair MDF File with EaseUS SQL Recovery

When the MDF file is corrupted or saved records are lost in the MDF file, you'll get this error on SQL. 

A fast and secure way to get rid of this issue is to repair the MDF file with a reliable SQL recovery tool. Notice that when you search online to find such a tool, choose the product provided by an experienced company. Also, it should be risk-free, 100% clean, and with a strong tech support team.

Being experienced in data recovery experience, EaseUS recently released its SQL recovery software to help SQL Server administrators.

EaseUS SQL Recovery Software

  • It is one of the most popular and effective ways to recover lost or corrupted data. 
  • It offers a variety of advantages, including the ability to recover data from both crashed and damaged databases
  • Additionally, it offers a user-friendly interface and is compatible with all major operating systems.

With it, you can effortlessly repair the corrupted database, and MDF file restores, and even restore deleted records in SQL. Follow the steps to repair the corrupted MDF file:

Step 1. Stop MS SQL Server service

Press "Windows + R" and enter services.msc.

Find and double-click "SQL Server (instant name)".

In the Properties windows, click "Stop" to end the SQL Server and click "Apply" to confirm.

Step 2. Run EaseUS SQL repair tool. In the main interface, click "Browse" (the two dots) to choose the corrupted MDF/NDF file. Then click "Repair" to start analyzing your MDF/NDF file. 

If you know the exact location of the file, click "Browse" to locate the database.

If you don’t know the file location, click "Search" to search for the .mdf or .ndf file in.

select the SQL database file

Step 3. When it has done, you will see all the database objects listed in the left pane of the window. Choose the database objects you'd like to repair and click "Export".

Select the database objects

Step 4. Choose a preferred way to export the database data: "Export to database" or "Export as SQL scripts". If you select "Export to database", you need to further select the server information, log into your account, and select a destination database, either a new one or an existing one.

export the SQL database objects

Step 5. Before you click "OK", now you need to restart the SQL Server.

Press "Windows + R" and enter services.msc.

Find and double-click "SQL Server (instant name)".

In the Properties windows, click "Start" to restart the SQL Server service and click "Apply" to confirm.

Step 6. Click "OK" to save the repaired files to your desired SQL database.

After saving the repaired MDF file, restart SQL Server and log in with your password. Then you should be able to access the MDF data and run SQL Server normally again.

Solution 2. Manually Resolve SQL Server Error 5171

Another method that you can use to run Microsoft SQL Server Management Studio to resolve this error manually:

Step 1. Run Microsoft SQL Server Management Studio and make sure the database is online. 

  • If it's offline, run the command: ALTER DATABASE mydb SET online.

Step 2. Modify MDF file information with ALTER DATABASE MODIFY FILE command.

  • Back up the SQL Server database first before you continue with the next step.

Step 3. Right-click on the currently running SQL Server and select "Stop".

Fix SQL Server error 5171.

Step 4. Copy the MDF and LDF files to a different directory.

Manually fix mdf is not the primary file in SQL Server.

Step 5. After that, restart the SQL Server and attach both MDF and LDF files.

Tips to Protect SQL SQL Database 

After resolving the SQL database 5171 error, it's also essential to learn useful tips to protect SQL Server database. Try the tips here for help:

1. Avoid improper upgrades of SQL Server

Don't upgrade SQL Server frequently. If the current version is running smoothly on your Server machine, stay with it. If you've upgraded the SQL but are having an error like 5171, run the sp_attch_db command to resolve this issue:

Fix SQL Server error 5171 due to imporper update

2. Back up SQL Server database regularly

Automated SQL Server backup software - EaseUS Todo Backup Advanced Server supports you to create a full backup of your huge SQL Server database with ease. 

3. Repair the corrupted SQL Server database immediately

Once the database is corrupted on SQL Server, apply EaseUS SQL Recovery to repair the database file and restore all valuable data immediately.


While SQL Server Database Error 5171 can be a frustrating and complex issue to deal with, there are many steps you can take to resolve it. Some common solutions include using SQL recovery software, such as EaseUS MS SQL Recovery, or fixing the SQL error manually. You may also want to consult with a database expert for additional guidance and support. Ultimately, the key is to stay calm, do your research, and take action as soon as possible in order to get your data back quickly and efficiently. With the right tools and strategies, SQL Server Database Error 5171 should not prevent you from accessing your important data again.

Consult with EaseUS Data Recovery Experts for one-on-one manual recovery service. We could offer the following services after a FREE diagnosis

  • Repair corrupted RAID structure, bootable Windows OS, and corrupted virtual disk files (.vmdk, .vhd, .vhdx, etc.).
  • Recover/repair lost partition and re-partitioned drive.
  • Unformat the hard drive and repair the raw drive(Bitlocker encrypted drive)
  • Fix disks that become GPT protected partitions

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EaseUS MS SQL Recovery

  • Restore (.mdf and.ndf) Files
  • Recover Corrupted Objects
  • Fix Database Log Files