Running PostgreSQL in a Xen DomU?

We're slowly trying to move away from hardware dependence for our
servers and it looks like Xen is the path.  Our primary goal is that if
a particular server fails, we can simply migrate the guest OSs to
another Xen node and the users will not experience any downtime.  Plus
it should allow us to consolidate a few servers.

Our database needs aren't that great at the moment, less then 50
concurrent users even at the worst of times.  But we might have
multi-gigabyte databases that will be queried in bursts and then left
alone for a few days.  A single CPU is generally fast enough for us.

So our current thinking is:

- Place PG in a DomU that can be moved from host-to-host as needed

- Backend storage would be over a SAN (iSCSI, 9k jumbo frames, dedicated
  NIC or bonded NICs for the SAN, dedicated switch or VLAN for the SAN)

- SAN unit itself would be DRBD'd to a 2nd SAN storage unit.  That's
down the road a bit once we build out the first few Xen nodes.

What I'm not sure of:

- Maybe it's better to run PGSQL in Dom0, on 2 different Xen units that
are beefed up, with a few lighter DomU guest OSs running in the
background.  Some sort of heartbeat software that allows the 2 Xen units
to grab the PGSQL's IP address as needed.

- Performance of PGSQL in a DomU.  What are the gotchas?  Do we need to
export PCI NICs to the PGSQL DomU?

(I have a lot of freedom to experiment.  As long as services are up and
running and things are stable...  We're going from individual machine
with DAS to a more clustered/virtual environment with SAN.)