Sizing Cluster

Hi There,
I have a question regarding sizing disk for kafka brokers. Let's say I
have systems capable of providing 10TB of storage, and they act as Kafka
brokers. If I were to deploy two of these nodes, and enable replication
in Kafka, would I actually have 10TB available for my producers to write
to? Is there any overhead I should be concerned with?

I guess I am just wanting to make sure that there are not any major
pitfalls in deploying a two-node cluster, versus say a 3-node cluster.

Any advice or best-practices would be very helpful!

Thanks in advance,
-pete