SQL Canada (SQLCAN)

Overview

SQL Server is a relational database management system, developed by Microsoft that is used for storage and retrieval of data whenever required. Database on SQL Server contains one master data file (MDF) and may be associated with number of new data file (NDF). Each MDF file is attached with a separate transaction log database (LDF). Sometimes, when user tries to attach the MDF/LDF database file, an Error may be encountered displaying error message “The header for file ‘xxx.mdf’ is not a valid database file header. The FILE SIZE property is incorrect. (SQL Server Error 5172)”The page will be discussing about the same error and solution on how to resolve MS SQL Error 5172.

What is Microsoft SQL Server Error 5172?

One of the most common error seen by the user of SQL Server while they are trying to attach the MDF or LDF Database from existing system to a new system. User needs to copy the database from the source system onto an external drive, attached the external drive to target system and copy them onto new system. Some of the possible causes of this error are damaged or corrupt log file/data file, attaching higher version database to a lower version SQL Server etc.

Precautions to Avoid MS SQL Error 5172

• The Database files of the source system should only be copied when SQL Server is properly shutdown or Database is detached.
• The Release and build number of SQL Server must be either exactly same for both source & target or the target must be higher. A database detached from SQL 2005 version needs to be attached to the same or higher version only.
• Presence of UNICODE type database attached to the target server, that user no longer wants to use. It should either be detached or renamed or delete it permanently.
• Attach the database file copied from source to target system using the sp_attach_db command or use SQL Server Management Studio while SQL Server is running. No files of an existing database should be replaced while SQL Server is down.

How to Fix SQL Server Header Error 5172

SQL Server Database files store their data as pages, each page is 8KB. The first page is called file header page containing the most important information about the whole file, like file signature, file size, compatibility, etc. Error occurs when certain value in header information in the boot page (page0) of LDF/MDF file is incorrect. It is also possible that file header page is damaged/corrupted making it unrecognizable by Microsoft SQL Server.

The user cannot attach the database without fixing the file header page manually. Let us consider a sample header of page 0:

Some of the modifications that need to be made in the above header file using Hex Editor are:

• Value at offset 0X00 (header version) should be 0X01
• Value at offset 0X01 (m_type) should be between 0X01 and 0X66
• Value at offset 0x04 (m_flagBits) should not be 0x02
• Value at offset 0x18 (m_objId) should be 0x63 or higher
• Combined value at offset 0x1E and 0x1F (m_freeData) should be 0x60 or higher (m_freeData is the offset where the next record will be placed)
• Page size (0x2000)– m_SlotCnt * 4 should be higher than m_freeData. If not, any subsequent operation will overwrite already existing data & is disaster to SQL Server and users.
• Offset 1C-1D (m_freeCnt) should be less than 0x1FA0 (8096). m_freeCnt denotes available free bytes within page, if it is greater then, SQL Server has reason to drop further execution because this will end up outside the 0x2000 boundary.
• value 0x1FA0 (8096) is derived from page size (8192) – total header byte size (0x60) = 96 = 8192 – 96 = 8096
• Offset 1E-1F (m_freeData) should not be zero
• Offset 16-17 (m_SlotCnt) should less than 0xFD0 (4048)
• The value at offset 0x40 thru 0x5F should be zero

After the changes made in the entries of header file using Hex Editor, user can try to re-attach the SQL Server Database files to overcome the issue of SQL Server Error 5172.

Conclusion

The blog will be discussing about one of the most common error encountered while user tries to attach their SQL Server Database files. The in-depth details of the SQL Server header error 5172 with the possible causes have been described. Some of the precautions that should be kept in mind are also discussed. The Error occurs when the header of the database file is invalid, which is why we need to make some modifications in the header file entries using Hex Editor.

The above elaborated description is sufficient enough, but if it fails to fix The header for file ‘xxx.mdf’ is not a valid database file header. The FILE SIZE property is incorrect then you can go with SQL Database Recovery Tool which allows you to recover data from corrupt database file.