An administrator is troubleshooting a vSAN issue. As part of the initial investigation, the following observations were identified: • vSAN cluster capacity is decreased. • Some virtual machine components are marked as degraded. • Component rebuild process started automatically. What is the cause of this issue?

A physical disk failure in a vSAN cluster directly causes the three observed symptoms. When a capacity disk fails, all vSAN components on it become unavailable, reducing the total cluster capacity. Any virtual machine object with components on that failed disk no longer meets its storage policy's availability requirements, causing it to be marked as "degraded." To restore policy compliance and data redundancy, vSAN's self-healing mechanism automatically initiates a rebuild process for the affected components on other healthy disks in the cluster after a default 60-minute delay.

A. VM migration to another cluster is in progress. This process moves data but does not cause existing components to be marked as degraded or trigger a failure-related rebuild.
B. vSAN license capacity is too small. A licensing issue would prevent the creation of new virtual machines or objects, but it would not impact the health of existing components.
C. Too many virtual machines were created in the vSAN cluster. This could lead to the datastore running out of space, but it would not cause healthy components to become degraded or initiate a rebuild.

1. VMware vSAN 8.0 Administration Guide, "vSAN Failure Scenarios," section "Failure of a Capacity Device."

This section explicitly states: "When a capacity device fails, vSAN marks all components on the disk as absent... After a 60-minute timeout, vSAN starts to rebuild the components on other hosts in the cluster." This directly links a disk failure to the component rebuild process. The failure of a capacity device inherently reduces the total cluster capacity.

2. VMware vSAN 8.0 Monitoring and Troubleshooting Guide, "Virtual Object Health," section "About vSAN Object Health."

This document defines the "Degraded" state: "The object is no longer fully compliant with the assigned storage policy, due to a failure. The object is still available." This confirms that a failure, such as a disk failure, is the cause of a degraded component state.

3. VMware vSAN 8.0 Administration Guide, "Monitoring vSAN with the vSphere Client," section "Monitor vSAN Capacity."

This section details how vSAN capacity is calculated and displayed. The failure and removal of a physical disk would be reflected as a decrease in the overall raw capacity of the vSAN datastore, aligning with the first observation.