Summary: This blog outlines possible reasons behind SQL Server database mdf file corruption. It also describes the manual process of repairing a corrupt MDF file of SQL Server Database, the challenges associated with the manual process, and the best alternative to overcome those challenges.
MDF is the primary data file of SQL Server Database that stores all data, including components such as Indexes, XML Indexes, Views, Tables, Triggers, and Stored Procedures. It is also known as the main or master database file of the SQL Server. Each SQL Server database would contain at least one MDF file.
The MDF file can be summed up as the primary element for administering the SQL database.
Several reasons lead to damage (corruption) in your SQL Server database file (.mdf). When this happens, the database becomes inaccessible and can result in potential data loss if the file is not repaired in time.
Before we discuss various solutions to repair an MDF file, let’s look at some of the common reasons that may result in SQL database file corruption.
Quick Fix: If you cannot risk losing data, use Stellar Repair for MS SQL software to repair corrupt MDF file and restore all its objects along with maintaining database integrity. The software is compatible with MS SQL Server 2019, 2017, 2016, 2014, 2012, 2008, 2008 R2 & older versions.
Possible Causes behind MDF File Corruption
Following are some common reasons that may result in a damaged MDF file in SQL Server:
- Sudden power failure
- Bugs in the server itself
- Faulty operating system
- Unexpected (abrupt) system shutdown
- Hardware issues, virus outbreak, etc.
- File stored on a corrupted external storage device
How to Repair MDF File?
Microsoft SQL Server provides built-in Database Console Command CHECKDB (DBCC CHECKDB) to test the physical and logical integrity of the db objects, by executing the following operations sequentially:
- Running DBCC CHECKALLOC command in the database.
- Running DBCC CHECKCATALOG command in the database.
- Running DBCC CHECKTABLE on each view and table in the database.
- Authenticating the content of each indexed view available in the database.
- Authenticating link-level constancy among table metadata, file system directories, and files when storing VARBINARY (max) data using FILESTREAM in the file system.
- Authenticating the Service Broker data in the database.
Note: Check the description of the above DBCC commands for more detailed information.
DBCC CHECKDB checks the consistency of db pages and other structure checks. It then reports errors, if any.
When DBCC CHECKDB reports database consistency errors, try to restore the db from a known good backup copy. But, if the backup is not available or is not the most recent one, CHECKDB provides several repair options to repair corrupt MDF file in SQL Server.
The Repair options are as follows:
- REPAIR_FAST – It maintains syntax for backward compatibility only; it does not help perform any repair actions. The syntax for this Repair option is:
DBCC CHECKDB (‘DB Name’, REPAIR_FAST)
- REPAIR_REBUILD – This repair option executes repair procedure that does not involve the risk of data loss. This can perform quick repairs, such as repairing the missing rows in non-clustered indexes, and even time-consuming repairs, such as the rebuilding of indexes. The syntax is:
DBCC CHECKDB (‘DB Name’, REPAIR_REBUILD)
Note: It (REPAIR_REBUILD) does not fix errors that include FILESTREAM data.
- REPAIR_ALLOW_DATA_LOSS – Microsoft recommends using this repair option as the last resort to fix all the errors. This is because even if the option repairs errors like deallocating a page, or row, etc., it may result in loss of data. The syntax is:
DBCC CHECKDB (‘DB Name’, REPAIR_ALLOW_DATA_LOSS)
Note: Use an alternative to DBCC CHECKDB ‘Repair_Allow_Data_Loss’ option to repair the corrupt MDF file without data loss.
Things to Consider When Using DBCC CHECKDB Repair Options
When using the DBCC CHECKDB repair options, make sure to take care of the following requirements:
- The first and foremost requirement is that the particular database should be in a single-user mode to run either of the three Repair commands. When a user does not set the database in single-user mode, the following error message occurs:
“Repair Statement is not processed. The database needs to be in Single user mode.
DBCC execution completed. If DBCC printed error messages, contact your system administrator.”
You can alter the SQL db into single user mode by the following command:
ALTER DATABASE DatabaseName SET SINGLE_USER WITH ROLLBACK IMMEDIATE
- Secondly, you must use the syntax to execute the DBCC CHECKDB repair commands correctly. It is only then that the discrepancies shall get fixed, resulting in a healthy database file.
- The DBCC repair statements are not validated memory-optimized tables. In such cases, i.e., if integrity issues occur in a memory-optimized table, you must restore the backup to gain access to the data in db file, provided the backup file is not in a damaged state.
The DBCC CHECKDB Repair Tool failed! What Next?
If the built-in DBCC CHECKDB fails to repair the SQL db file, the next thing that you can do is run a specialized SQL repair software such as Stellar Repair for MS SQL. The software helps to repair MDF file and extract the data stored within it, without spending a lot of time &efforts in writing complex code.
This SQL repair software helps in scanning the db for mangled entries, correcting bit patterns, and bringing db to a consistent state.
Key features of Stellar Repair for MS SQL Software
- Repairs corrupt MDF and NDF files
- Recovers all database components, such as tables, keys, triggers, stored procedures, etc.
- Supports recovery of deleted records from SQL Server database
- Previews recoverable database objects
- Provides multiple options to save repaired SQL db files in MS SQL, XLS, CSV, and HTML formats
When a MDF file turns corrupt, the only concern of system administrators or database administrators (DBAs) is to ensure that the database is accessible and that all the data is restored to its original, intact state.
You can easily restore the database file from the most recent backup copy, but if it is not available or damaged, running DBCC CHECKDB with repair options may help. If none of the repair options work for you, or you don’t want to risk losing data by running the “REPAIR_ALLOW_Data_LOSS” option, using Stellar Repair for MS SQL software is the best approach for repairing corrupt MDF file of SQL Server Database. It can help repair database files (.mdf and .ndf) when DBCC CHECKDB repair fails.