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Introduction
vSAN cluster partition issues in VxRail environments can severely impact your virtualized infrastructure, leading to data unavailability and potential VM downtime. A cluster partition occurs when ESXi hosts within your VxRail cluster lose network communication with each other, splitting the cluster into isolated sub-groups. This comprehensive guide will walk you through identifying, troubleshooting, and resolving vSAN cluster partition issues in Dell EMC VxRail systems.
Understanding vSAN Cluster Partitions
A vSAN cluster partition happens when hosts in your VxRail cluster cannot communicate properly over the vSAN network. Instead of functioning as a unified cluster, the system splits into multiple network partitions where hosts within each partition can communicate with each other but not with hosts in other partitions. This fragmentation can render vSAN objects unavailable and compromise your storage infrastructure’s reliability.
Common Symptoms of vSAN Cluster Partition
Before diving into resolution steps, identify if you’re experiencing a cluster partition by looking for these symptoms:
- vSAN cluster partition alarm displayed in vSphere Client or Skyline Health
- Network partition warning in vSAN Health Service showing multiple partitions detected
- Nodes showing as “network partitioned” despite successful ping tests via vmkping
- Sub-Cluster Member Count showing 1 when running
esxcli vsan cluster geton individual hosts - vSAN network configuration status indicating “network misconfiguration detected”
- Empty output when running
esxcli vsan network listcommand - ESXi UI showing vSAN traffic disabled for vmk3 (or your designated vSAN VMkernel adapter)
Root Causes of vSAN Cluster Partitions in VxRail
Understanding the underlying causes helps prevent future occurrences:
1. VMkernel Adapter Misconfiguration
The most common cause in VxRail environments is the vSAN VMkernel adapter (typically vmk3) becoming untagged for vSAN traffic, especially after cluster shutdown and restart operations.
2. Invalid or Incomplete Unicast Agent List
In unicast mode deployments, an incorrect unicast agent list can cause hosts to be unable to discover other cluster members.
3. Network Configuration Issues
- Mismatched subnets across ESXi hosts
- VLAN configuration errors
- Incorrect MTU settings
- Physical network connectivity problems
4. Network Overload and Packet Loss
Excessive dropped packets due to network congestion can trigger partition detection, even when physical connectivity exists.
5. ESXi Version Mismatch
Different ESXi versions running on vSAN nodes can cause compatibility issues leading to partitions.
Step-by-Step Resolution Guide
Method 1: Resolving VMkernel Adapter Issues (Most Common)
This is the primary solution for VxRail clusters experiencing partitions after power events.
Step 1: Verify vSAN Network Configuration
Connect to each ESXi host via SSH and run:
esxcli vsan network listIf the output is empty, vmk3 is not tagged for vSAN traffic.
Step 2: Check Cluster Status
Run the following command on each host:
esxcli vsan cluster getLook for the “Sub-Cluster Member Count” field. If it shows “1” on each host, they’re all in separate partitions.
Step 3: Re-tag VMkernel Adapter for vSAN Traffic
On each affected node, execute:
esxcli vsan network ip add -i vmk3Replace vmk3 with your actual vSAN VMkernel adapter name if different.
Step 4: Verify Resolution
After tagging all hosts, verify the configuration:
esxcli vsan network listYou should now see vmk3 listed with the correct IP address. Check cluster membership:
esxcli vsan cluster getThe “Sub-Cluster Member Count” should now reflect the total number of hosts in your cluster.
Method 2: Fixing Unicast Agent List Issues
If your VxRail cluster uses unicast mode and hosts can ping each other but remain partitioned, the unicast agent list may be corrupted.
Step 1: Enable Ignore Cluster Member List Updates
On all hosts, run:
esxcfg-advcfg -s 1 /VSAN/IgnoreClusterMemberListUpdatesThis prevents the incorrect list from being propagated during the fix.
Step 2: Verify Current Unicast Agent List
Check the existing unicast agent list:
esxcli vsan cluster unicastagent listStep 3: Rebuild the Unicast Agent List
Remove all existing entries and add the correct ones. For each host in the cluster:
esxcli vsan cluster unicastagent remove -u esxcli vsan cluster unicastagent add -u -U -p 12321Step 4: Restore Default Settings
Once all hosts have the correct unicast agent list:
esxcfg-advcfg -s 0 /VSAN/IgnoreClusterMemberListUpdatesMethod 3: Network Connectivity Troubleshooting
Step 1: Verify VMkernel Network Configuration
List all VMkernel adapters:
esxcfg-vmknic -l | grep vmk3Ensure the vSAN VMkernel adapter has the correct IP address, subnet mask, and VLAN configuration.
Step 2: Test Network Connectivity
Perform ping tests from each host to all other hosts using the vSAN VMkernel adapter:
vmkping -I vmk3Step 3: Check for Packet Loss
Use esxtop to monitor dropped packets:
esxtopPress ‘n’ for network view and examine the %DRPRX field for excessive dropped packets.
Step 4: Verify MTU Settings
Test jumbo frames if configured:
vmkping -I vmk3 -s 8972 -dMethod 4: Using vSAN Health Service for Diagnosis
Step 1: Access vSAN Health Service
In vSphere Client, navigate to:
- Cluster → Monitor → vSAN → Health
Step 2: Review Network Health Checks
Examine these specific health checks:
- Network Health – vSAN Cluster Partition
- Network Health – All hosts have a vSAN vmknic configured
- Network Health – Hosts small ping test (connectivity check)
- Network Health – Hosts large ping test (MTU check)
Step 3: Check vSAN Disk Management View
Navigate to vSAN Disk Management and examine the “Network Partition Group” column to identify which hosts are in which partition.
Step 4: Address Identified Issues
Follow the recommendations provided by each failed health check to resolve underlying problems.
Prevention Best Practices
1. Implement Proper Shutdown Procedures
Always follow Dell EMC’s recommended shutdown and startup procedures for VxRail clusters to prevent VMkernel adapter configuration loss.
2. Regular Health Monitoring
- Enable vSAN Health Service and review it regularly
- Configure vSAN Skyline Health for proactive monitoring
- Set up alerts for network partition detection
3. Network Infrastructure Maintenance
- Ensure redundant network paths are properly configured
- Regularly update switch firmware
- Monitor network utilization to prevent congestion
4. Configuration Management
- Document your vSAN network configuration
- Use configuration backup and restore procedures
- Maintain consistent ESXi versions across all hosts
5. Validate After Maintenance
After any maintenance activity, verify:
- vSAN network configuration is intact
- All hosts show in a single partition
- Health checks pass successfully
Troubleshooting Tips
If Hosts Can Ping But Remain Partitioned
This typically indicates a unicast agent list issue or VMkernel adapter misconfiguration rather than physical network problems. Focus on Methods 1 and 2 above.
If Only One Host is Partitioned
Isolate troubleshooting to that specific host:
- Check physical network connections
- Verify switch port configuration
- Review host-specific VMkernel settings
- Check for host-level firewall rules blocking vSAN traffic
If Partition Occurs After Firmware Updates
- Verify all hosts completed the update successfully
- Check for ESXi version compatibility
- Review update logs for errors
- Consider rolling back if issues persist
Logs Specifically Needed for a vSAN Partition Event
When the issue is vSAN network partition, the most critical logs are:
Top Priority Logs
vobd.log– shows partition detection, host join/leave, DOM electionsvsanmgmt.log(host + vCenter) – object/component impactvmkernel.log– NIC link flaps, vmk migrations, MTU issueshostd.log– host networking and switch changesvsanvpd.log+ lsom.log – disk group behavior during isolation- NSX logs (if uplink changes caused isolation)
Verification and Validation
After implementing any resolution, perform these validation steps:
- Verify Single Partition: All hosts should show the same Sub-Cluster UUID and the total member count
- Check vSAN Health: All network health checks should pass
- Test VM Operations: Create a test VM and verify storage operations work correctly
- Monitor for Stability: Observe the cluster for 24-48 hours to ensure the partition doesn’t recur
When to Contact Support
Contact Dell EMC Support if:
- Partition issues persist after following all resolution steps
- Physical network infrastructure problems are suspected
- Multiple health checks fail simultaneously
- Data unavailability or VM downtime occurs
- You’re unsure about making configuration changes in production
Conclusion
vSAN cluster partition issues in VxRail environments are typically caused by VMkernel adapter misconfiguration, especially after power events, or unicast agent list corruption. By following this systematic troubleshooting approach, you can quickly identify and resolve partition issues, restoring your VxRail cluster to full operational status. Regular monitoring and adherence to best practices will help prevent future occurrences and maintain a stable, high-performance vSAN infrastructure.
Remember to always test resolution procedures in a non-production environment when possible and maintain current backups before making configuration changes. With proper understanding and proactive management, you can minimize the impact of vSAN cluster partition issues on your VxRail infrastructure.
Keywords: vSAN cluster partition, VxRail troubleshooting, VMkernel adapter configuration, vSAN network partition, Dell EMC VxRail, ESXi cluster partition, vSAN health service, unicast agent list, vmk3 configuration, VxRail cluster issues
