Quota and User Management - Getting Started with Red Hat Enterprise Virtualization - page 147

6. Under the Storage section of the same window, use the green slider to set Stor-
age Threshold and the blue slider to set Storage Grace . Then, click on the Edit
button in bottom-right corner, and limit the storage size from unlimited to a limit
set by Quota.
Here, the threshold is like the soft limit; exceeding this will generate a warning.
Grace is like a hard limit and exceeding it will prevent further resource usage.
Quota must be selected for all objects under the data center. For example, if you
try to start a virtual machine, keeping Quota in the Audit mode, you will receive
a warning stating that Missing Quota for VM VMNAME, proceeding since in
Permissive (Audit) mode under the Events tab before the virtual machine is
powered on. If Quota is set to the Enforcing mode, the virtual machine will fail
to start unless Quota is selected for the virtual machine and its virtual disks.