Fault Tolerant Postgresql (two machines, two postmasters, one disk array)

Sorry if this is a FAQ, I did search and couldn't find much.

I need to make my Postgresql installation fault tolerant.
I was imagining a RAIDed disk array that is accessible from two
(or multiple) computers, with a postmaster running on each computer.
(Hardware upgrades could then be done to each computer at different
times without losing access to the database).

Is this possible?

Is there another way to do this I should be looking at?

Thanks,

j