In VMware vSAN environments, maintaining data availability and compliance is critical. One of the more nuanced health states you may encounter is “Reduced Availability with No Rebuild.” For server Administrators, understanding this state is essential for proactive infrastructure management and avoiding unexpected data loss.
What Does “Reduced Availability with No Rebuild” Mean?
This vSAN object health state indicates that a component has failed or become unavailable, but vSAN is unable to initiate a rebuild. Despite this, the object remains accessible, and I/O continues to flow. However, the object is no longer compliant with its assigned storage policy, and data is at risk if another failure occurs.
Why No Rebuild Happens
vSAN may skip the rebuild process due to:
Insufficient fault domains: For example, FTT=1 RAID-1 requires at least 3 fault domains.
Lack of free capacity: vSAN needs enough space to rebuild components. VMware recommends maintaining at least 30% free capacity in the vSAN datastore.
Host rebuild threshold exceeded: If used space surpasses this threshold, vSAN may not be able to restore data after a host failure.
Network partition or disk failure: These can prevent vSAN from identifying a suitable rebuild target.
Object States That Lead to This Condition
| Object State | Description |
|---|---|
| Absent | Component temporarily unavailable (e.g., host reboot). |
| Degraded | Component failed due to disk or path error. |
| Reduced Availability with No Rebuild | Object is accessible but cannot be rebuilt due to resource constraints. |
| Inaccessible | All replicas are unavailable—VMs using the object are offline. |
The Role of the Object Repair Timer
vSAN uses a repair delay timer (default: 60 minutes) to avoid unnecessary rebuilds during transient failures. If the failed component doesn’t return within this window, vSAN attempts a rebuild. But if rebuild conditions aren’t met (e.g., not enough hosts or capacity), the object enters the Reduced Availability with No Rebuild state.
You can adjust this timer using the vsan.clomRepairDelay advanced setting.
How to Resolve the Issue
Check Cluster Capacity
Ensure at least 30% free space is available in the vSAN datastore.
Review the host rebuild reserve threshold.
Verify Fault Domains
Confirm that the cluster meets the minimum host count for your FTT and RAID level.
Inspect Network and Disk Health
Use vSAN Health Service to check for network partitions or disk failures.
Use CLI for Deeper Diagnostics
bash# localcli vsan debug object health summary getMaintenance Mode Precheck
Run a datastore evacuation precheck to ensure placing a host in maintenance mode won’t cause data loss.
Monitoring and Prevention
Use vCenter > Monitor > vSAN > Resyncing Objects to track rebuild status.
Integrate vRealize Operations or custom dashboards for proactive alerting.
Regularly validate storage policy compliance and cluster health.
