During a File and Folder, SQL, Exchange Information Store, or System State backup a specific file or group of files fail to back up. In the backup job logs, those files present the following error:
Intelliblox signature generation failed for ___.
The delta signatures that our software relies on to take incremental backups were unable to be generated and stored in system memory.
These failures may occur sporadically but if they happen frequently, they are more likely to happen for backups that run longer.
Explanation
The module used by the Intronis software to calculate the changed blocks in a file is called Intelliblox. Intelliblox relies on Remote Differential Compression (RDC) to do this calculation. The Intelliblox engine will scan the blocks belonging to a file being backed up and filter out only those blocks which have changed to include in an incremental backup. For most backups, Intelliblox will scan over the shadow copy created at the beginning of the backup but for System State backups or for File and Folder backups that have Snapshot Mode turned off, Intelliblox will scan the actual files.
When Intelliblox is calculating the sum of changed blocks, it creates a signature file to record the changed blocks for each individual file. The signature files are created in the "Signatures" folder in the software's installation directory and are typically a fraction of the size of the changed blocks they correspond to.
When the Intelliblox signature generation fails, the most common cause is related to the source material of the generation process: the shadow copy. If the shadow copy gets deleted or is aborted, the signature generation will be interrupted and will cause all incomplete or untouched files to fail the backup.
Resolution
Shadow Copy Aborts Prematurely
If the shadow copy the backup is running off of aborts before the backup is finished, the incident is logged in Event Viewer. Shadow copies may abort prematurely for a few reasons: high I/O load, insufficient storage space, displacement by other shadow copies, or manual deletion to name a few. If you see the shadow copy was aborted or deleted around the time the signature generation errors appear, try increasing the shadow copy storage allocation. If that does not fix it you will need to tackle the specific reason the shadow copies are aborting.
Low Disk Space or Memory
Intelliblox signature generation failure can also be caused by low disk space. If there is little free space on the drive containing the "Signatures" folder then signatures cannot be created. Also, if there is less than the required temporary space for a backup this may also cause the signature generation to fail.
Signature generation requires memory proportional to the number of changed blocks recorded for a single signature. The greater the number of changed blocks the more memory that may be required during the generation. If the computer performing the backup has high memory utilization, this may also cause signature generation failures. Generally, memory shortages only become a potential problem for larger files (>5 GB).