Need opinions for ScaleUp or ScaleOut

Question

Hi all,
i've need some advise for resolve my doubt on RAC, because i have to
sizing RAC environment in my business.
Have been shows me two different solutions of RAC:
1) Two nodes of Bl680c (until 4 CPU quad Core)
2) Four nodes of Bl480c (only 2 CPU quad Core)
First solution is correct sure but is more expensive and i would like
to know if his cost is justifiable, more cpu are effective benefit?
So if bl480c server with dual CPU have cost of 6.000$ and bl680c with
4 CPU is 12.500$ (double), in RAC environment it is better 2 nodes of
bl680c or 3-4 nodes of bl480c ?
thanks for advices
Andrew

Answer 1

Scale-Up is the ability of your configuration to sustain the same response time when both the workload and resources increase proportionally.
Scale-up is 'usually' achieved by increasing the amount of hardware resources i.e. CPU and memory.
Scale-out is related to adding hardware resources by adding another node.
Sometimes, depending of app. design, the scale-up option on existing hardware can be more efficient than scale-out.
Simple explanation to this is related to the overheads associated with maintaining RAC cache coherency and DB locks between the nodes/instances which will occupy the available resources and 'take it away' from application.
The mail goal which you would like to achieve (I assume) is that the application can scale. You should understand that correctly configured RAC system will give you higher availability than single-instance on single-hardware configuration, but it is not at the same time guarantee that your application will scale too.
So, if you consider your design from scalability point of view you should consider it in terms of application response times.
hth,
goran