VMware HA is a VMware solution for high-availability of virtual machines to protect against host failures, hardware failures, operating system (OS) crashes.

Using VCS virtual-to-virtual or in-guest clustering in a VMware environments provides high availability of applications inside the guest by providing protection from host failures, hardware failures, OS crashes and also application failures at software layer. For example, in cases of application hang, file-level corruption at the OS level cannot be resolved with a reboot.

Since there is a cost involved in maintaining standby virtual machines (VMs), you may choose to protect only specific applications using VCS in-guest and protect the remaining applications using VMware HA. By using VMware HA in conjunction with VCS in the guest, when a host fails, standy VCS nodes running on that host are automatically restarted by VMware HA on a new host without the need for user-intervention, potentially eliminating the need to maintain multiple standbys.

See Assessing availability levels for Symantec Cluster Server in the VMware guest.