If you are only using a single cluster to back a Provider/Org vDC for allocation pools, the suggestion is to upgrade to 5.1.2. This will enable SCAP mode, and set the reservations on the resource pool. We may need to use a tool to perform a remediation for the reservations, but that's pretty straight forward.
This is the release note about SCAP:
- Allocation pool organization virtual datacenters can be elastic or non-elastic: Starting with vCloud Director 5.1.2, system administrators can configure Allocation Pool organization virtual datacenters with Single Cluster Allocation Pool (SCAP), making them non-elastic. This is a global setting that affects all Allocation Pool organization virtual datacenters. By default, Allocation Pool organization virtual datacenters have Single Cluster Allocation Pool enabled. Systems upgraded from vCloud Director 5.1 that have Allocation Pool organization virtual dataceters with virtual machines spanning multiple resource pools have Single Cluster Allocation Pool disabled by default.To change the Single Cluster Allocation Pool setting go to System > Administration > General > Miscellaneous. Before enabling Single Cluster Allocation Pool, migrate any virtual machines on secondary resource pools to the organization virtual datacenter's primary resource pool.