Data Domain: Veeam Backup Fails When Maximum Opened Connection Limit Is Reached

Backup operations fail while attempting to connect to a DD Boost storage unit.

Administrators may observe one or more of the following:

Backup jobs fail during storage initialization.
Backup jobs fail before data transfer begins.
Connection attempts to the DD Boost storage unit are rejected.
Repeated storage access failures despite the Data Domain system being online and healthy.
Errors indicating the maximum number of allowed connections has been exceeded.

Example Backup Application Log

BackupJob_Task.log

Failed to connect to storage. Maximum number of opened connections cannot exceed 60.
Storage: dd-system01, User: backup_service
Failed to create or extend backup chain on target storage.

Example DD Boost Client Log

DDBoost_Client.log

Max allowed connections exceeded.
Connection to storage failed.
Failed to access backup file path on the storage unit.

This issue is typically caused by limitations within the backup application and not by the Data Domain system.

Certain backup software versions enforce limits on the number of restore points that can exist within forward incremental or forever forward incremental backup chains when using DD Boost storage.

Supported backup chain limits include:

Version 11: Maximum of 60 restore points.
Version 12: Maximum of 120 restore points.
Version 13: Maximum of 120 restore points.

If a backup chain exceeds the supported limit for the installed version, the application may be unable to establish additional storage connections and can generate errors such as:

Maximum number of opened connections cannot exceed 60.
Max allowed connections exceeded.
Failed to connect to storage.

As a result, backup jobs may fail even though the Data Domain system and DD Boost services are functioning normally.

Review the backup application's retention settings, backup chain configuration, and software version to ensure that backup chains remain within the supported limits for the deployed release.

Recommended actions:

Verify the backup application version currently in use.
Confirm the backup chain length does not exceed supported limits:
Version 11: 60 restore points.
Version 12: 120 restore points.
Version 13: 120 restore points.
Schedule periodic active full or synthetic full backups to split long backup chains into shorter segments.
Adjust retention settings where necessary to prevent backup chains from exceeding supported limits.
Review backup job configuration and retention policies for compliance with vendor best practices.
Consider upgrading to a newer supported version if higher backup chain limits are required.
If additional validation is needed, consult the backup vendor's official documentation and administration guides for the applicable software version.

Example Log References
BackupJob_Task.log
Failed to connect to storage. Maximum number of opened connections cannot exceed 60.
Storage: dd-system01, User: backup_service.
DDBoost_Client.log
Max allowed connections exceeded.
Connection to storage failed: maximum connection threshold reached.