Re: allow servers to access to the same data

i want that the main pc save two identical databases, the first database will be saved on local hard drive and the second database will be saved on a nas.
if the main pc has a failover, a second pc will be turned up with the same ip and access to the database on the nas

How do you intend to get the main pc to save two identical databases?

I wouldn't recommend running Pg off a NAS file system like NFS or CIFS.

This plan is fragile and failure prone. I very strongly recommend that you use replication instead. See

  http://www.postgresql.org/docs/current/static/high-availability.html
  http://wiki.postgresql.org/wiki/Shared_Storage

--
Craig Ringer