"Reduced Availability with No Rebuild" in vSAN object health

Products

• VMware vSAN

Issue/Introduction

vSAN Skyline health in vCenter UI will report the health of all the objects in the vSAN cluster.

"Reduced availability with no rebuild" health state indicates that the object has suffered a failure, and unable to rebuild the failed component.

vSAN objects will still be accessible. However, object data is at risk if additional failures occur.  

 

vSAN object health can be validated from ESXi CLI of any host in the cluster using the below command.

# localcli vsan debug object health summary get

Environment

VMware vSAN 6.x
VMware vSAN 7.x
VMware vSAN 8.x

Cause

Rebuild operations cannot proceed because of resource constraints such as insufficient capacity or an inadequate number of fault domains.

Below are the minimum number of Fault domain or Standalone hosts:

FTT=1 RAID-1 requires minimum 3 fault domain or 3 standalone hosts 

FTT=1 RAID-5 requires minimum 4 fault domain or 4 standalone hosts

FTT=2 RAID-6 requires minimum 6 fault domain or 6 standalone hosts

Resolution

Maintain adequate free capacity in the vSAN datastore, with a 30% free capacity being the recommended threshold. Ensure that the datastore utilization does not exceed the host rebuild threshold.

For more details on managing capacity, refer to the following document:
Reserved Capacity in vSAN Cluster

• Host rebuild threshold: This defines the space required by vSAN to tolerate a host failure. If the used space exceeds this threshold and a host fails, vSAN may be unable to restore all data from the failed host.

Potential resource constraints on the host may arise due to various reasons, including:

• Network partition: vSAN Health Service - Network Health
• Host failures: vSAN Health Service - Host Failures
• Disk failures: Troubleshooting vSAN OSA Disk Issues
• vSAN Decommissioned State: Inaccessible VMs due to vSAN Node Decommission

 

If the issue cannot be isolated or resolved using the above steps, please contact Broadcom Support for further assistance.

 

 

Note: You may encounter a situation where the vSAN cluster displays a "Reduced Availability with No Rebuild" warning. Upon further investigation, you will see this error is reported for vSAN objects on a single host, even though all objects are otherwise in a healthy state. 

Skyline Health might report an error for multiple objects in a vSAN cluster: "Reduced availability with no rebuild."

All vSAN objects are accessible.

The command line output for problematic esxi host, shows all objects in reduced availability with no rebuild state.

# localcli vsan debug object health summary get

If the remaining hosts in the vSAN cluster displays all objects are in healthy state, then follow the below mentioned steps:

• Perform a datastore evacuation precheck on the affected host to verify that placing it in maintenance mode would not render any objects inaccessible.
• Place the host in maintenance mode using the Ensure Accessible option.
• Reboot the host to resolve the issue.

Note: Before rebooting a host make sure all object in vSAN cluster is in healthy state and accessible.