When performing full and incremental backups of Microsoft Sharepoint SQL databases, the incremental backups may be larger than expected. In some cases these incremental backups may be nearly as large as full backups.
The change block backup method used by the Backup Exec Sharepoint agent for Sharepoint SQL databases will back up changed blocks for the SQL databases based on a bitmap of changes provided by the SQL server hosting the Sharepoint databases.
There is no bitmap provided for the database log file, filestream, or full text catalog files so those must be backed up in their entirety during the incremental backup.
This is a normal functionality for the Backup Exec Sharepoint agent.