What is the best type of server and operating system for mega networks?

We will get Blade with chasis for high end applications and we can use redhat linux for enterprise deployments

I think dell have a great servers like , r720 , t420 i used them  in various jobs for database , virtualization , they are working fine .

For O.S , its depend on what you will use at this systems , microsoft have many tools for administration tasks , also  linux is stable , and troubleshooting in linux more easy because system depend on txt files in every service, any file corupt you can get the correct file and replace it , even if the kernel fail you can recopy kernel form System CD and start system again.

Hope this help.

I will suggest Dell Server/ series for small or medium business as i m using several of them with minimum requirement of attention ( no much hardware failures ) as far is windows is concern i am using and with Hyper-V  as the server is vastly upgrade able in memory and storage space.

Dear you go for dell R920 server with4 socket processor Its performance is great. 

Database

Salam, 

It depends what service you are going to run on Server and what application you are going to deploy for your orginisation.