When you create an SDDC, you can choose to have it contain medium or large SDDC appliance configurations. An SDDC with a medium appliance configuration can be scaled up (upsized) to large. An SDDC that has a large appliance configuration cannot be scaled down to medium nor can its management cluster scale down below three hosts.
Large-sized appliances are not supported for two-host SDDCs with stretched or conventional clusters. Large-sized appliances cannot be scaled down.
You can use a control on the SDDC Settings tab to upsize a medium-sized SDDC to a large-sized one. This change is permanent and cannot be undone. If there aren’t enough free resources available, the operation adds a host to the SDDC.
The upsize workflow includes a vCenter re-start and an NSX failover. It typically incurs 15-20 minutes of management plane downtime, and could take longer if a disk check or manual intervention is needed. During this downtime, the vCenter UI will not be available and you won’t be able to add or remove hosts or execute VM power operations. Running workloads continue to run, and vSphere HA continues to protect VMs that are already powered on. The NSX Edge failover causes a 10-15 second interruption of North-South connectivity.
This operation cannot be performed while SDDC maintenance, including the addition or removal of hosts, is underway.
Prerequisites
Verify that the SDDC has at least three hosts in each AZ that it occupies. A stretched-cluster SDDC requires at least six hosts in the management cluster (three in each AZ).