Storage foundation 6.0 Cluster file system in Linux

Hi,

I need the help..

Iam new to Veritas Storage foundation in cluster environment,

for our Client, new implementation.

we are planning to configura Veritas storage foundation Cluster file system 6.0 for Linux.

2 Linux server with 3 disk shared.

Planning to install storage foundation for VCS, CVM, CFS on Linux for some of the application to use this server.

My question is, in  Veritas storage foundation Cluster file system, I/O fencing is neccessary to configure, if yes, can you please tell me.

Why, its needed and how to configure with 3 shared disk.

Thank you,