Availability storage in failover cluster

Why is the "Availability storage" resource group in my failover cluster marked as Down?

The Resource Groups tab in Site24x7 (Server > Windows Cluster > click on the monitor) lists all the resource groups in a failover cluster and monitors their current status. 'Available Storage' is one of the resource groups in Windows Failover cluster. 
In the failover cluster, if there is no unused cluster disk, 'Available Storage' will be reported as Down. Execute the below PowerShell command to see the status of the resource groups.

Refer the other performance metrics that are provided for monitoring the failover clusters.