VMware vSphere identifies and manages all its objects: VMs, ESXi hosts, networks, data stores, resource pools, etc. using the MoRef ID (Managed Object Reference Identifier). MoRef IDs are allocated to virtual machines and other objects incrementally by vCenter.

When Zerto maps an environment within vCenter for its configuration and operations, for example when creating a VPG, it acquires and maps the MoRef IDs of the available virtual machines, and refers to these MoRef IDs in its own environment management and replication operations.

If an ESXi host is removed from inventory and is then re-added, everything that was on it gets a new MoRef ID. As a result, a virtual machine, protected by Zerto that was running on that host will be allocated a new MoRef ID. The new MoRef ID would not be known to the Zerto Virtual Manager, and the virtual machine would no longer be protected. The same result applies to the VRA, which becomes a ghost VRA, unknown to the Zerto Virtual Manager.

In order to avoid these issues Zerto Virtual Replication maintains the old MoRef ID map containing the original MoRef IDs as well as unique identifiers of the hosts and VMs. Zerto Virtual Manager constantly monitors the vCenter environment and maintains a mapping of MoRef IDs - new to original.

The re-mapping of MoRef IDs can take several minutes. When system administration tasks require the importing of VPG definitions of a host that was removed and then re-added, it is advisable to wait approximately 5 minutes from when the host was re-added before performing the import of the VPGs.