Two approaches can be taken to manage datastore space usage and make sure that there is always enough free space for VMs to run: vCenter space usage alarms and the Storage Distributed Resource Scheduler (SDRS) feature.

SDRS has been described in the Balancing storage utilization recipe in Chapter 5, Optimizing Resource Usage. It is a more advanced approach, which allows completely automating VM migrations. At the same time, this feature requires the Enterprise Plus license, which may not be needed for all environments.

A more simple approach is vCenter alarms. vCenter has default alarm definitions related to datastore space usage. Configured with email notifications, they allow administrators to react proactively and move VMs around to avoid "out of free space" situation. Alarms only notify administrators about conditions, so there is no option to automate any actions. At the same time, this feature does not require any additional license.

By default...