you can check iCanCloud (http://icancloudsim.org/) which is written in C++ on the top of OMNeT++ and INET frameworks.

iCanCloud is a simulation platform aimed to model and simulate cloud computing systems.

Download link: http://www.arcos.inf.uc3m.es/~icancloud/Home.html

If you are simulating a storage area network in data center, then sansim is an option

http://www.simsans.org/

I hope you can modify it to simulate other data center architectures.

You can use

SimSANs v4.0 and OMNeT++

http://www.simsans.org