How to Fix Damaged MDF and LDF files in SQL Server

This post is intended to explain the importance and functionalities of MDF and LDF file in an SQL Server, along with common reasons due to which they go corrupt. The section further discusses ways to repair these damaged files.

Introduction of SQL Server Files

MDF NDF And LDF FilesSQL Server by Microsoft is a database management system. The system stores and helps retrieve data as and when requested by other applications. There are mainly three files in this server namely – MDF, NDF, and LDF. First two files are the primary and secondary database of the server respectively. The third one is used for storing logs of database transactions.

Although both log and data files are accessible by the same server, the two are not stored on the same location. Although both files are related with SQL, here we will only talk about repairing corrupted .mdf and .ldf files.

Primary & Log File for Database

Primary database is also called Main Database file. Hence, the abbreviation MDF! It’s the main file of the SQL server. SQL Server database contains only one MDF file which houses elements like stored procedures, views, triggers, etc. One can also say that this file is the primary component required for successfully administering SQL database.

Log Database File (LDF) is the one that maintains the logs of whatever activities or transactions have happened in the SQL server. The file is extremely important in restoring server data in the event of a disaster such as critical errors or data corruption. The size limit of this file is defined at the time when database is designed.

Corruption of MDF and LDF Files

The biggest priority of any database administrator is to ensure the safety of the server. Otherwise smallest mishap could lead to loss of data that can sometimes be extremely hard to recover and restore. There are countless reasons that can cause these two kinds of files to become damaged. However, some of the most common ones are:

  • The first and foremost reason why an MDF or LDF file might become corrupt is because of the limited storage size. If the data on the disk exceeds its limit, there is a higher likelihood of either of these files becoming corrupt.
  • If some modifications are made in the SQL server during DROP OPERATION, this can increase the chances of damage to these files.
  • Sometimes certain hardware related issues can also cause corruption of these files. The issues can be bad sectors on the disk, or some hard drive related issues.
  • Virus attack, as we all know, can also be a major cause of server issues including corrupted MDF and LDF file.

Manually Repair MDF and LDF files

Fix MDF And LDF FilesIn case either of these files is damaged, users can try running DBCC CHECKDB command. If the reason for file damage is some logical corruption, this command might help you recover data from the server. The process involves running a code in the server to repair the files.

Use SQL Server Recovery Software

If you do some research online, you can find several SQL recovery software/tools that help recover data by restoring the MDF and LDF files. Other than file repair, these tools provide several other functionalities as well. Depending on requirements, you can go for the one that you find most suitable.

Author Introduction:

Peter Song is a data recovery expert in DataNumen, Inc., which is the world leader in data recovery technologies, including outlook recovery and PDF recovery software products. For more information, visit

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