dual power for hadoop in datacenter?

[Koert Kuipers]

what are the thoughts on running a hadoop cluster in a datacenter with
respect to power? should all the boxes have redundant power supplies and be
on dual power? or just dual power for the namenode, secondary namenode, and
hbase master, and then perhaps switch the power source per rack for the
slaves to provide resilience to a power failure? or even just run
everything on single power and accept the risk that everything can do down
at once?