Issue
Backups for a protected endpoint surface a warning or fail with the error message, "Error 326: Fast delta failed."
Environment
NinjaOne Device Backup
Cause
An Image backup job was unable to reference the previous shadow copy used by the backup agent. NinjaOne needs this information to optimize the current backup job's efficiency in terms of speed and size.
Common Causes include:
- Another application is deleting/modifying existing Volume Shadow Copy Service (VSS) snapshots.
There is not enough storage space allocated for the volume to maintain both VSS snapshots.
The larger the volume or amount of data change between backups, the more storage space you'll need.
Resolution
VSS needs to be healthy and have the amount of space necessary to keep both the current and previous backup jobs' VSS snapshots. In most cases, you'll encounter this error if you have not allocated enough disk space for shadow copy storage. We recommend a 20 percent allocation be allowed, but it can be dependent on the size of the disk, the amount of change per backup, and other factors. We have seen machines with only three percent available to shadow copies never have a problem, and some with 20 percent that need a bit more because of the data churn on the disk.
For additional information about VSS issues, refer to:
To view a more detailed illustration of the process, you can download the JPG file attached to this document.
Additional Resources
For additional troubleshooting guidance, refer to: