What is Error 9721?
Windows System Error Code 9721, known as DNS_ERROR_DNAME_COLLISION, is a Cluster & Storage error that occurs during cluster, backup, and storage management. The error indicates that: A DNAME record already exists for given name. When this error is encountered, the Windows operating system was unable to complete the requested operation within the storage/cluster services subsystem. The error code 9721 is returned by the GetLastError() function and provides developers with a specific identifier to diagnose the root cause of the failure. The symbolic name DNS_ERROR_DNAME_COLLISION maps directly to this numeric code and is commonly referenced in Microsoft documentation, developer forums, and system logs. Understanding this error and its context within cluster, backup, and storage management is essential for effective troubleshooting.
Common Causes
- System resource conflict: A DNAME record already exists for given name.
- Quorum lost due to node failure
- Storage paths disconnected
- Cluster service dependency failure
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Read the full guide →Step-by-Step Solutions
- Open PowerShell as Administrator
- Run: Get-ClusterNode to check node status
- Run: Test-Cluster for full validation
- Review the HTML report for issues
Video Tutorials
Diagnostic Command
Run this PowerShell command to find related events in your system log:
Get-EventLog -LogName System -Newest 20 | Where-Object {$_.Message -like "*9721*" -or $_.Message -like "*DNS_ERROR_DNAME_COLLISION*"} | Format-List💡 Open PowerShell as Administrator, paste the command above, and press Enter.
Prevention Tips
- Configure redundant storage paths (MPIO)
- Validate cluster after updates
- Monitor disk latency and capacity