vSAN capacity utilization alarm 'What if the most consumed host fails'

Products

• VMware vSAN

Issue/Introduction

This health check simulates the impact of a single ESXi host failure in a vSAN cluster. It checks two things:

1. Loss of Resources :  When a host fails, its cache and capacity resources become unavailable.

2. Rebuild Simulation : vSAN tries to rebuild the affected components to maintain redundancy.

The check also calculates how the cluster would be affected if the host using the most resources goes down. It shows how much resource usage would shift to the remaining hosts and how much capacity would still be available.

Environment

VMware vSAN 8.0.x
VMware vSAN 7.0.x

Cause

This issue occurs because the cluster may not have enough free resources to handle the failure of a heavily loaded ESXi host. When a host fails, vSAN needs to rebuild components to maintain redundancy, but if there isn't enough available capacity on the remaining hosts, it could lead to reduced performance or data availability risks.

Resolution

If this health check fails, it indicates that the cluster may not have sufficient capacity to absorb the workload and re-protect affected components following an ESXi host failure. To ensure vSAN can successfully rebuild objects and maintain the configured storage policy compliance, consider adding additional capacity or hosts to the cluster.

References Technical document :  Add a Capacity Device to vSAN Disk Group

• Navigate to the

  vSAN

  cluster.
• Click the

  Configure

  tab.
• Under

  vSAN

  , click

  Disk Management

  .
• Select a disk group.
• Click the

  Add Disks

  at the bottom of the page.
• Select the capacity device that you want to add to the disk group.
• Click

  OK

  or

  Add

  .