What level of responsiveness does your site need?
For some organizations, it is sufficient to use a scripted set of manual procedures in the event of a primary site failure. Others need the remote site to be active in rather short periods of time (minutes). For these organizations, the need for Veritas remote site failover software or some equivalent is overriding.
Also, do not allow the software to automatically failover from the primary site to the backup site. The possibility for false positive detection of failure of the primary site from the secondary site is too high. Instead, configure the software to monitor the primary site and alert you when it detects a failure. Then, confirm that the failure has happened before beginning the automated process of failing over to the backup site.
How much data must be preserved and how quickly must it be made available?
Although this seems like a simple question, the ramifications of the answer are large. Variations in scenarios, from the simple to the most complete, introduce quite a difference in terms of the costs for hardware, network data infrastructure, and maintenance.