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Summary : The article addresses SQL Server error code 2515, a restoration problem caused by unmarked differences in LSN and differential base LSN in the bitmap. Solutions involve checking hardware faults, restoring from backup, running DBCC CHECKDB (with potential data loss), or utilizing tools like Kernel for SQL Server Recovery for secure data recovery.

Creating a backup is crucial for recovering database objects in the event of database file corruption. SQL Server offers a unique identifier, Log Sequence Number (LSN), which serves as a recovery point during the database restoration process.

LSN also facilitates the execution of a differential backup. During a differential backup, a corresponding bitmap is generated, marking all changes made during the backup process. Any alterations not captured in the bitmap result in database errors.

Utilizing this differential backup, damaged database objects can be effortlessly restored. However, occasionally, during the restoration process, you might encounter the following error message:

Server: Msg 2515, Level 16, State 1

Page P_ID, object ID O_ID, index ID I_ID have been modified but are not marked modified in the differential backup bitmap.

It has a symbolic name DBDC_DIFF__MAP__OUT_OF_SYNC

Explanation of SQL error 2515

The error indicates that the page has a higher Log Sequence Number (LSN) than the reference LSN in the differential backup or the differential base LSN. However, despite this, the page is not marked as modified in the differential backup bitmap.

Solutions for SQL error 2515

The mentioned error occurs when the modifications in LSN (Log Sequence Number) and differential base LSN in FCB or the differential reference LSN in Backup Manager are not indicated in the bitmap. Restoring a corrupted database can be a challenging task. However, the following steps can guide you in the recovery process:

Check for hardware faults

If the problem is caused by hardware issues, resolving it involves replacing the problematic hardware. Begin by examining the system, application logs, and SQL error logs to pinpoint the specific problem. Subsequently, replace the faulty hardware components or consider changing the entire hardware setup to resolve the issue effectively.

Restore from backup

If the SQL server continues to display the error even after hardware replacement, attempt to restore the database from a known good backup.


If no useful backup available, run DBDC CHECHDB without a repair clause. It will help you assess the error situation and its magnitude. Later you can run the DBDC CHECKDB with this REPAIR clause to fix the issue. However, you should expect the possibility of data loss in this case.

Try SQL Recovery tools

Running the DBCC CHECKDB tool can lead to undesirable data loss. To prevent such situations, consider using an efficient data recovery tool like Kernel for SQL Server Recovery. This tool is capable of repairing corrupted MDF/NDF files of all sizes and versions, ensuring a smooth recovery process without compromising your data.


In this discussion, we explored SQL Server error code “2515,” which arises during the restoration process through Log Sequence Number when differences between LSN and differential base LSN are not marked in the bitmap. Solutions for addressing this issue were presented, including utilizing backups, investigating hardware issues, executing DBCC CHECKDB commands, and ultimately resorting to third-party SQL Server recovery tools. We highly recommend a trustworthy SQL Server Database Repair tool to tackle such challenges effectively.

Kernel for SQL Database Recovery