May 2015 | SansSQL

Thursday, May 21, 2015

Restore database from corrupt SQL database backup file - Another Guest Post by Jyoti Prakash

Often people have corruption issues regarding Microsoft's SQL server database as well as its backup. Basically, backup is the only way to make your database secured and protective; it helps you to restore your inaccessible files of the main database when any type of corruption or damage occurs. But, what if backup also corrupt, while attempting to restore database from backup file. There could be multiple reasons behind such disaster situation, here in this write-up you will get to know about the reason and solutions behind such case, where SQL Server user faces corruption in SQL Server database backup and not able to restore their databases.

How and why the backup file gets corrupt:     

SQL backup files are basically a replica of your original SQL database, which can be located in different locations on the system. There could be multiple reasons of inaccessible backup file. Here are some most common causes of damaged SQL BAK files:

  • Virus attack
  • Abrupt system shutdown
  • Use of a wrong driver
  • Bad sectors in your system's hard disk
  • Sudden removal of a selected tables, records, and procedures
  • unconventional functioning of Hard disk
  • Improper shutdown of application
  • Wrong database synchronization
  • System crash
  • corrupt database system rules and tables
The most common error message during restoration of database is: 'Backup or restore operation terminating abnormally.'

A Backup restoration error occurs when a filemark in the backup device could not be read. There could be multiple causes of when a user encounters a filemark error. The most common reasons are:
  • A media failure may arise on the same device where the backup is stored
  • A write failure may occur while creating the backup file
  • Loss of connectivity may arise while creating a network backup
  • A failure in the Input/Output path occurs in the disk just after successful write to the disk

Manual Solution:
After backup restore error the first thing you could do is to check whether all the sets of backup have issues or just some sets have issues. It might be possible that only some sets of backup have issues due to which you are getting restore error. In order to retrieve other backup sets from the device, you need to specify the file number. In case, there are multiple backup sets available on a single device, then to determine the usable backup, you can run the following query:


If you got the usable set from the disk, copy it to another drive for usage and try to restore the damaged files with the help of SQL restore commands. Here are some of the SQL commands that you can use to restore corruption in your SQL database backup.                                 

To recover a database use the following command. This will put your database in the "restoring" state

RESTORE DATABASE <DB Name> FROM DISK='<Backup Location>' WITH FILE = <FileNumber>

Note: Write the backup set number instead of 'FileNumber' that you want to restore.

The following command will take the database, which is in 'restoring' state and make it available for end users.

RESTORE LOG <DB Name> FROM DISK = '<Backup Location>'

The above mentioned commands are used to restore corrupt backup file of SQL database. However, these corrupt backup recovery solutions provided by Microsoft are not applicable for deep corruption cases. In order to restore your highly damaged or corrupt SQL backup database you can always choose a third party SQL backup recovery software. These professional utilities are designed to restore data from a corrupt (.BAK) SQL backup file.  

Third party applications have functions to restore SQL backup file due to all above mentioned reasons. Before buying any professional backup recovery tool, you need to choose the most reliable one. For that you should use the online demo versions of the backup recovery applications to test their efficiency.

Jyoti is a Sr. DBA - SQL Server at Stellar Data Recovery and has written several article on SQL Server disaster recovery planning & fixing. In addition, she spend her time on Technical forums helping people with the issues related to SQL server.