Knowledge Base

In some situations the last compressed data block fails to be written to disk

Category: Troubleshooting & error messages
Date: 07 Apr 2009
Product: SQL Backup
Versions: 5.1 and 5.2 (Server Components)
Fix Version: 5.3 (Server Components)

There is a critical bug affecting SQL Backup 5.1 and 5.2. What may happen in some situations is that the last compressed data block fails to be written to disk. SQL Backup will report system error 87 (The parameter is incorrect), and the backup file is incomplete. This happens when the last block of compressed data is less than 512 bytes in size (usually). Given that the average size of the last block of compressed data is 2 MB (4 MB is the max), the probability of this happenning is 0.02%.

This bug has been addressed in SQL Backup 5.3.

If it is impractical to upgrade the software in a timely manner, you may attempt to convert the backup file to native MTF format and restore it from SQL Server Management Studio.
The file itself may still be usable after conversion to MTF format, as the tail of a backup file contains Microsoft Tape Format data which isn't actually used by SQL Server if it is not available. For a users' file that was tested, the conversion to MTF will report an error, due to the absence of the last block, but SQL Server will still restore the file.