Inconsistent thresholds between vSphere alarm "Datastore usage on disk" and vSAN health check "Storage space"

Products

• VMware vSAN

Issue/Introduction

Symptoms:
The vSphere alarm "Datastore usage on disk" and the vSAN Health check "Storage" monitor the vSAN datastore usage, do not show consistent alarm when the usage reaches default threshold values.

Cause

The vSphere alarm and the vSAN Health check have different default thresholds, and both of them support threshold customization, hence they are inconsistent with each other.

Resolution

To resolve this issue, use the vSAN Health check > Capacity utilization > Storage space, formally called Disk Space in 7.0U1 and below, to monitor vSAN datastore usage, because it is more efficient in monitoring vSAN space:

• The default thresholds are computed by the specific configurations of the hosts, which is more efficient.
• The vSphere alarm only supports setting thresholds applying all kinds of datastores, but the vSAN Health alarm support setting different thresholds for vSAN datastore and vSAN Direct datastore.
• The vSAN Health threshold customization integrates effectively with capacity reserve. The percentage will always be applied to the available capacity.

To avoid inconsistency, you can disable the vSphere alarm "Datastore usage on disk" on vSAN datastore, and trust the vSAN Health check alarm.

• To disable the vSphere alarm on vSAN datastore:

1. Go to vsanDatastore > Configure > Alarm Definitions and select Datastore usage on disk.
2. Click DISABLE.