clustering and/or failover?

thinking in the long-term for my project...

i'm looking at trying to set up two database servers with
some sort of clustering and/or failover that are talking
to a SAN. is this even feasible using postgres?

using ms sql server as an example (because that is what
my office is currently using) you can set up two database
servers that will check each other's heartbeat to see if
they are both up. if one goes down then the other takes
over responding to requests. you can also set up a
cluster that will have both machines responding to
requests concurrently.

with the data set up on a fibre channel raid box you
don't have to worry about replication, you just have to
make sure that the data is properly locked by each of
the servers (in the clustering example) so that no two
machines are updating the same data at the same time.

i am fairly certain that postgres cannot handle the
first example (heartbeats) but am wondering if it can
handle the second example where two instances are
hitting the same physical data store.

many thanks!

rjsjr