Primary server failures
A single primary server for each NetBackup domain controls all the backup activity within the domain. Thus, the primary server represents the most obvious single point of failure in the data protection environment. Without the primary server, backups and restores are not possible. To protect NetBackup against such failures, the primary servers must be highly available.
More information about installing and configuring NetBackup on these cluster technologies is available in the NetBackup Clustered Primary Server Administrator's Guide.
https://www.veritas.com/docs/DOC5332
The primary servers that are running in virtual machines can be protected using the Hypervisor's high availability tools. For details refer to http://www.veritas.com/docs/000006177.