VMware Clusters

A cluster is a group of tightly coupled hosts that work closely together so that in many respects they can be viewed as though they are a single computer. Clusters are used for high availability and load balancing. With a cluster, you define two or more physical machines that will provide resources for the hosts that are assigned to that cluster. By using clusters, you can achieve high availability and load balancing of virtual machines. Load balancing is referred to as DRS (Distributed Resource Scheduler) by VMware.

■ If one of the physical hosts goes down, the other physical host starts up the VMs that the original host was running (high availability).

Both of these features use vMotion to move these virtual guests from one system to another.

You cannot apply high availability nor DRS to a Virtual Replication Appliance (VRA).

VMware high availability decreases downtime and improves reliability with business continuity by enabling another ESX/ESXi host to start up virtual machines that were running on another ESX/ESXi host that went down.

High availability is automatically disabled by Zerto while updating recovered virtual machines in the recovery site from the VRA journal. After the promotion of the data from the journal to the virtual machine completes, high availability is automatically re-enabled.

The HA configuration can include admission control to prevent virtual machines being started if they violate availability constraints. If this is the case, then a failover, test failover or migration of the virtual machines in a VPG to the cluster with this configuration will fail, if the availability constraints are violated when the virtual machines are recovered. It is recommended to test the failover, as described in “Testing Recovery”, on page 324, to ensure recovery will succeed, even when HA is configured with admission control.

VMware DRS enables balancing computing workloads with available resources in a cluster.

DRS is automatically disabled by Zerto while updating recovered virtual machines in the recovery site from the journal for these recovered virtual machines. After the promotion of the data from the journal to the recovered virtual machine completes, DRS is automatically re-enabled.

If DRS is disabled for the site, VMware removes all resource pools in the site. If the recovery was defined to a resource pool, recovery will be to any one of the hosts in the recovery site with a VRA installed on it.

Note: If the site is defined in Zerto Cloud Manager, only a resource pool can be specified and the resource pool must also have been defined in Zerto Cloud Manager. For details about Zerto Cloud Manager, refer to Zerto Cloud Manager Administration Guide.