vSAN Data Resync After Exiting Ensure Accessibility Maintenance Mode
Article ID: 435985
Updated On:
Products
Issue/Introduction
Administrators observe vSAN resynchronization activity immediately after an ESXi host exits Maintenance Mode when the "Ensure Accessibility" option was utilized. Additionally, clarification is required regarding the functional differences between vSAN data evacuation options ("Ensure Accessibility", "No Data Migration", and "Full Data Migration") and the architectural risks associated with utilizing "No Data Migration".
Environment
VMware vSAN
Cause
When a host is placed into Maintenance Mode using "Ensure Accessibility", vSAN components residing on that host are marked as absent but are not fully evacuated to other nodes. During the maintenance window, active guest OS writes continue to the remaining component replicas in the cluster. Upon the host's return, vSAN automatically detects that the returning components are stale and initiates a delta resync to copy the missing writes, thereby restoring full Storage Policy (FTT) compliance.
Resolution
No corrective action is required for the delta resync. Allow the synchronization task to complete naturally to restore full fault tolerance to the cluster.
To determine the appropriate maintenance mode strategy for future operations, adhere to the following architectural definitions and recommendations:
Ensure Accessibility (Default/Recommended for Standard Maintenance): vSAN ensures that all accessible virtual machines remain accessible by guaranteeing at least one full active replica of the VM data remains in the cluster. During this state, full redundancy (e.g., FTT=1) is temporarily sacrificed to minimize evacuation time and storage capacity overhead. A delta resync is strictly expected upon host return.
No Data Migration (Not Recommended): vSAN does not evacuate any data from the host prior to entering Maintenance Mode. Risk: This option is highly discouraged in production environments. If the cluster cannot satisfy the availability requirements with the remaining active hosts, virtual machines will become completely inaccessible and experience immediate downtime.
Full Data Migration: vSAN evacuates all data components from the target host to other active hosts in the cluster. This option maintains the current availability and redundancy (FTT) policies during the entire maintenance window but requires the most time and necessitates sufficient free capacity across the remaining cluster nodes.
Additional Information
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