About protecting against master server failures
A single master server for each NetBackup domain controls all the backup activity within the domain. Thus, the master server represents the most obvious single point of failure in the data protection environment. Without the master server, backups and restores are not possible. To protect NetBackup against such failures, the master servers must be highly available.
More information about installing and configuring NetBackup on these cluster technologies is available in the NetBackup Clustered Master Server Administrator's Guide.
https://www.veritas.com/support/en_US/article.DOC5332
The master 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.