What Does “vSphere HA Virtual Machine Failover Failed” Mean?
The error “vsphere ha virtual machine failover failed: Acknowledge, Reset To Green” is a common alert in VMware environments, often appearing in vCenter during or after a host failure event.
This alert indicates that vSphere High Availability (HA) attempted to restart a virtual machine on another host but failed to complete the failover. However, it does not always mean the VM is down or unavailable. In some scenarios, it is expected behavior that poses no threat to your virtual machines or cluster reliability.
Common Causes of vSphere HA Failover Failure
Below are the common causes of the error:
- Host isolation or network partition: One of the most frequent reasons for failover failure is host isolation, where a host loses network connectivity but is still running. because the original VM is still active and holding disk locks, the failover attempt may fail to prevent a split-brain condition.
- Storage or datastore accessibility issue: vSphere HA requires shared storage access across all hosts. If a datastore is not accessible, failover cannot proceed.
- Insufficient cluster resources: Failover requires available CPU and memory resources on other hosts in the cluster. Failover may fail if the cluster is running at high utilization or the resource reservations are too high.
- vCLS (vSphere Cluster Services) VM issues: Modern versions of VMware vSphere rely on vCLS (vSphere Cluster Services) VMs to maintain cluster health and DRS functionality.
- HA Agent or cluster configuration: Each host in the cluster runs an HA agent responsible for communication and failover coordination. Failures can occur if there is HA agent or cluster configuration problem.
- Misconfiguration or Compatibility Problems: Sometimes the issue is specific to the virtual machine itself. For example, a VM configured with an unsupported hardware version, CPU compatibility issues (EVC not configured properly), a mounted ISO, or device locks preventing restart.
How to Fix VMware “vSphere HA virtual machine failover failed.”
Here we provide the following 6 methods to help you fix this vSphere HA failover error.
Fix 1. Clear the Alarm
Use these steps to dismiss the alert when VMs remain operational on the original host
Step 1. Log in to vCenter Server via the vSphere client. And navigate to the Monitor tab, and click “Issues and Alarms” > “Triggered Alarms”.
Step 2. Choose the vSphere HA virtual machine failover failed alert and select “Acknowledge”.
Step 3. Select the affected VM/host cluster in the inventory navigator.
Step 4. Go to “Monitor” > “Triggered Alarms”. Right-click the specific alarm and select “Reset to Green“.
Step 5. Navigate to Hosts and Clusters and select the target cluster.
Step 6. Click the “Configure” tab > “Services” > “vSphere Availability”.
Step 7. Toggle the service off, wait for completion, then toggle on.
Fix 2. Resolve Network Isolation Issues
Start with the network layer, as many failover failures are caused by host isolation rather than actual host crashes.
✯ Verify Management Network Connectivity
1. Access the ESXi host’s DCUI (Direct Console User Interface) or use SSH.
2. Run vmkping <isolation_address> to test connectivity from the VMkernel adapter.
3. Check physical switches/ports for link status, VLAN tagging, and firewall rules (ensure ports 8182 TCP/UDP are open for HA heartbeats) .
✯ Adjust Isolation Response (If Needed)
1. Navigate to the cluster > “Configure” > “vSphere Availability” > “Edit”.
2. Under Host Isolation Response, select an alternative (e.g., Shut down guest OS) if Leave powered on is causing lock conflicts .
For custom isolation addresses, set das.usedefaultisolationaddress to false and configure das.isolationaddress[1-10].
✯ Check Datastore Heartbeats
1. In the cluster’s vSphere Availability settings, verify Datastore heartbeating is enabled.
2. Select at least two shared datastores accessible by all hosts to ensure redundancy.
Fix 3. Fix Inaccessible ISO/CD-DVD Attachments (vSphere 7.x/8.x)
This resolves failures where other hosts cannot access an ISO stored on a local-only datastore.
Step 1. Right-click the affected VM > “Edit Settings” > “Virtual Hardware”. Locate the VM/DVD Drive device.
Step 2. Uncheck “Connected” and “Connect at power on” to disable the device. Alternatively, change the “Media” setting from “Datastore ISO File” to “Client Device” or “Host Device”.
Step 3. Click “OK” to save changes.
Fix 4. Troubleshoot vCLS VM inaccessibility
vSphere Cluster Services (vCLS) VMs are required for DRS/HA functionality. Their unavailability blocks failover VMware Support Portal.
Step 1. Navigate to the affected ESXi host in the vSphere Client > Virtual Machines.
Step 2. Identify the inaccessible vCLS VMs (they typically have a prefix of “vcls-“) that are powered off or marked as missing.
Step 3. Right-click each inaccessible vCLS VM and select “Remove from inventory” to clear the invalid entry.
Step 4. If the vCLS VMs cannot be removed, temporarily disable DRS: navigating to the cluster > “Configure” > “DRS” > “Edit and toggling DRS Off”.
Step 5. Reboot the vCenter Server Appliance (VCSA) to trigger the automatic redeployment of vCLS VMs.
Step 6: For persistent issues, enable the ESXi shell and run the command esxcli system cls vm destroy –all to manually destroy stuck vCLS VMs.
Step 7: Re-enable DRS and wait 5–10 minutes for the vCLS VMs to restart automatically.
Step 8: Run esxcli storage file system list to check for mount errors and ensure physical network connectivity for vCLS communication.
Fix 5. Restore Degrade VM Storage Connectivity
Failover fails when healthy hosts cannot access VM disks or configuration files due to degraded storage; follow these sequential steps to restore connectivity.
Step 1. On all hosts in the cluster, run the command esxcli storage core device list to confirm that shared datastores are properly mounted and free of errors.
Step 2: Check for PDL (Permanent Device Loss) or APD (All Paths Down) errors in the ESXi host logs, which indicate critical storage issues.
Step 3: Inspect SAN/NAS/fibre channel switches for proper zoning, link status, and healthy GBIC/cable connections.
Step 4: Verify that the storage array is presenting LUNs correctly and that all ESXi hosts in the cluster have read/write permissions to the affected datastores.
Step 5: For VxRail clusters specifically, run the command vdq -qh to identify any storage drive failures that may be causing degradation.
Step 6: Ensure storage fault isolation by separating storage and management networks to prevent cross-network issues.
Step 7: If admission control is blocking failover due to storage constraints, navigate to the cluster > “Configure” > “vSphere Availability” > “Edit” > “Admission Control”, enable “Override calculated failover capacity“, and set it to 33% to temporarily bypass the constraint while resolving storage issues.
Fix 6. Reconfigure vSphere HA (Last Resort)
If all other methods fail to resolve the “vsphere ha virtual machine failover failed” error, use this sequential method to reset the HA configuration.
Step 1: Navigate to the cluster in the vSphere Client > “Configure” > “vSphere Availability” > “Edit”.
Step 2: Toggle vSphere HA to Off and click OK, then wait for the task to complete fully.
Step 3: Return to the same vSphere Availability settings menu and toggle vSphere HA back to On.
Step 4: Reconfigure any advanced HA settings (such as admission control, isolation response, or datastore heartbeating) to match your cluster’s requirements.
Step 5: Monitor the cluster for 10–15 minutes to ensure HA is operational and no new failover alerts are triggered.
Strengthen Failover Reliability with i2Availability
While VMware vSphere HA is essential for maintaining availability, it has clear limitations:
- It restarts VMs, rather than ensuring continuous availability
- It depends heavily on cluster health (network, storage, resources)
- It cannot prevent issues like failover delays, restart failures, or split-brain risks
This is exactly why errors like “vsphere ha virtual machine failover failed” occur.
For organizations that require near-zero downtime and guaranteed failover, a more advanced solution is needed.
Here, we would like to introduce Info2Soft’s i2Availability. This is an enterprise-grade high availability and disaster recovery solution designed to provide continuous application protection, not just VM restart.
i2Availability continuously replicates data with byte-level accuracy to the standby vSphere environment. Once the main server is confirmed to have failed, the standby environment will take over the business immediately.
Advantages of i2Availability:
- Seamless Failover: With byte-level and real-time data replication to sync VM data between production and disaster recovery hosts. When a host fails or network/storage issues occur, it automatically switches applications to a standby host in seconds, ensuring low RPO and RTO.
- Intelligent Fault Detection: Uses multi-heartbeat monitoring, node arbitration, and disk arbitration to prevent false failovers and split-brain scenarios. Supports custom scripts for automated application start/stop, combined with virtual IP failover to achieve sub-second switchover.
- Simplified Management: i2Availability features an intuitive graphical interface that centralizes monitoring of your vSphere cluster, VM status, and HA events—eliminating the need to manually check fdm.log or hostd.log files for errors.
- Enhanced Reliability for Critical Applications: Designed for enterprise-grade reliability, i2Availability ensures 99.99% uptime for your core applications (ERP, databases, payment gateways) by combining virtual IP drift technology and customized scripts to automate application recovery.
Best Practices to Prevent HA Failover Failures
Preventing the “vsphere ha virtual machine failover failed” error is not about a single fix—it’s about building a resilient HA architecture across network, storage, and compute layers.
Below are proven best practices to minimize failover failures and ensure reliable recovery in VMware vSphere environments.
Design for True HA (Not Just Enabled HA)
Simply enabling HA is not enough,your cluster must be designed to support failover under real conditions.
Best practices:
- Use shared storage accessible by all hosts (SAN, NAS, or vSAN)
- Follow N+1 capacity planning (at least one host worth of spare resources)
- Avoid single points of failure in compute, storage, and networking
Build Network Redundancy for HA Stability
Network issues are one of the top causes of false failover attempts. Please ensure HA agents can always communicate reliably across hosts.
What to implement:
- Redundant management network interfaces (NIC teaming)
- Dedicated HA heartbeat network
- Multiple network paths to avoid isolation events
Ensure Consistent and Accessible Storage
Storage accessibility is critical for successful failover. So it is suggested to guarantee that any host can restart any VM when needed.
Key actions:
- Verify all datastores are mounted on every host
- Avoid placing HA-protected VMs on local storage
- Configure datastore heartbeating properly
- Monitor storage latency and connectivity
Optimize HA and Admission Control Settings
Misconfigured HA policies can silently block failover.
Recommendations:
- Enable and properly configure Admission Control
- Choose a policy that matches your workload (e.g., percentage-based)
- Avoid overly strict resource reservations
- Use EVC (Enhanced vMotion Compatibility) for CPU consistency
Maintain Healthy HA and vCLS Components
Unhealthy cluster services can lead to false alarms or failed failovers, so cluster services need to be remain stable for HA to function correctly.
Checklist:
- Ensure HA agents are running on all hosts
- Monitor cluster state (avoid “reconfiguring HA” loops)
- Verify vCLS VMs are: Powered on and evenly distributed across hosts
Test Failover Regularly (Don’t Assume It Works)
Many environments only discover HA issues during real outages. So testing failover regularly can ensure your HA setup works as expected under real conditions.
Best practice:
- Perform planned failover tests (simulate host failure)
- Validate VM restart behavior and timing
- Review HA logs and alerts after testing
Combine HA with Backup and DR Solutions
HA alone does not guarantee full protection.
Limitations of HA:
- Cannot prevent data corruption
- Cannot recover from ransomware or logical errors
- May fail under infrastructure constraints
Recommendation: Please combine an enterprise backup solution and advanced HA/DR tools like i2Availability
Conclusion
The “vsphere ha virtual machine failover failed” alert is one of the most commonly misunderstood issues in VMware vSphere environments. While it may look critical at first, it doesn’t always indicate an actual outage, but it should never be ignored without proper validation.
The key is to approach troubleshooting systematically—starting from infrastructure and moving up to configuration and VM-level checks. More importantly, this alert highlights a deeper reality: vSphere HA is designed for availability, not guaranteed continuity. It relies on restart-based recovery, which can fail under real-world conditions.
In addition, to minimize downtime and risk, you can use Info2Soft‘s solutions to create a professional DR strategy and regularly backup VMware VMs.