The key point on what to use is depending on your system footprint an requirements, plus of course your inhouse skills.
Speaking genererally from Oracle technical archtict / dba view, you will be facing yourself the following questions:
- How much overhead do I want to have on support?
You naturally will have worse reaction times on non-Oracle platforms, like specially IBM Pseries as well as HP Itanium (due to historical reasons)
- What Service do I need provide and which technologies do I want to use?
Generally you shouldn't mix things having the same purpose like eg. RAC and virtualization, as this increases layers and eventually Cost.
You can nowerdays do great things with eg. Oracle VM (Xen) on x86-64 and Oracle Dataguard (eventually with Active Dataguard Option). Keep it simple and focused
RAC is for most companies too complicated to manage, as mostly it is not properly implemented. Also it only protects you against host failures => you still have the shared storage to be taken care of.
As most RAC installations iv'e seen in the past 10 years are based on "conventional wisdom", they are mainly 2 node clusters. Reason is simple: License Cost / Habits
So more simpler and valueable combination is too use Oracle VM for HA, which enables you to even do live migration of hosts in maintenance windows plus Oracle Dataguard for site failures. As you Dataguard you can offload backups to standby site to not bother users.
This is just one example, which works well for 11g OLTP Databases, put can also be applicated to DW Databases, if you take more care about availability than performance.
Reading Concepts Guide at Oracle, will certainly point you to a solutions that works for you.
When planning with virtualization technologies you should also consider not to consolidate too much into too little machines. You won't like to find yourself in situation, where you consolidated everything in 2 big fat enterprise level machines and the suddenly one breaks, which makes you loose 50% of your total capacity. Rather go for more, put smaller servers for multiple reasons:
Capacity on demand on big IBM, HP, SUN machines sounds good at first, but it turns out to be quite expensive after a few years, if you need to buy old RAM modules
At some extend you still need to shut down even those boxes and phyiscally upgrade anyway
If you really have technical problems with one server, you still have the other ones and you have more time with less performance & customer impact to replace the faulty one
As said as dba normally you have to deal more with bad application bugs, i/o contention, network issues. For I/O contention it does not make a big difference wheither you wait with a 4.7Ghz IBM Power 6 or a Intel 1.6 Ghz Itanium for I/O. You cannot wait faster. In such case you rather invest into a PCI-E SSD, if you really cannot handle the hot data block by re-design / tune the Application.