Need to build a small business server cluster for the purpose of crunching data. It will not host a web site that needs to be available 24/7.

• It does need to support servers that host Redis, a Cassandra database cluster, and a Python web server. Operating system will most likely be Centos 6.4
• Other servers in the cluster should be able to communicate very fast with each other, especially the Redis server. This will probably require the use of internal IP addresses.
• We will need to use multi-data center replication to synchronize the Cassandra cluster with the one that we currently have hosted on the cloud

Was looking into network switches and we are unsure of the appropriate specifications that we should be looking for.

• Does the switch need to be "managed" or can it be "unmanged"?
• Does the switch need to support IPv6 or just IPv4?
• Do we need an enterprise level Cisco switch, or can we go with something like a $200 DLink managed (or unmanaged) small business switch?

Thanks so much!