We covered a lot of ground in this article and it should serve as an introduction to 9iRAC on cheap Linux hardware. There are plenty of other topics to dig into including tuning, backup, SQL*Net setup and Load Balancing, I/O Fencing, NIC Failover and so on.
9iRAC is *NOT* a silver bullet as any good DBA knows. It will protect you from a single instance failure because of memory, kernel panic, or an interconnect failure, but there are still cases where your database could go down, for instance if the cluster manager software fails, or you lose a datafile either from human error, or a storage subsystem problem. Further redundancy can help you, but there are risks associated with an accidentally deleted object, or even and Oracle software bug.
Take a look at some of the documents listed below for further reading.