Windchill cluster and vault connected to two hosts? what type of vault storage i must use to connect vault to master and slave, it has to be accessed(read,write) from both at the same time -right?? SAN, NAS , NFS?

Correct, you should have read-write permission from all the hosts including the master. You can either have two different hosts with its individual host names or  with single cluster name in vault configuration and mount the vault with respective to the path it sees from each hosts. You can use SAN/NAS or NFS. I have used for NFS and filers for Windchill vault and both works fine, we had actual write speed of about 40 mb/sec.

PTC has recommendations on this here - https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS61023

Regards

Binesh Kumar