Which one its Better in Oracle ERP e-Business suite IBM Server POWER 8 vs SUN SPARC T4-2 ? Why ?

Now Sun Hardware belongs to Oracle and this is an advantage, because Oracle is optimizing the hardware for Oracle Software, and you will get full support for the Hardware, OS, database and application ...  

sun SPARC T4-2 is better. Because this server in the application tier and the SPARC T4-4 server in the database tier are only about half utilized providing significant headroom for additional Oracle E-Business Suite R12.1.2 processing modules and future growth.

IBM Power 8 and Sun Sparc t4-2 both are the best for their own performance and process handling, but I prefer you can go for Sun Sparc T4-2 , why because when or by chance if you require any kind of OEM support during your production outage you no need to go for Run behind two OEM's to trouble shoot, Oracle will Collabrate both the support engineers and gives you an fast and easy resolution.

Each type has its advantages and disadvantages, They are based in the same work

In the end, in Saudi Arabia there is superiority of Sun servers because of suppliers and technical support

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This depend on many factors.

Current Database - number of users - preferred platform  

the beast is Oracle Sparc 

Normally it depends on the market. Here in Saudi Arabia I found Oracle ERP e-Business Suite.