Cassandra is designed to be run in the cloud or on commodity hardware, so (relative to relational databases) you usually don't need to worry about breaking the bank on expensive, heavy-duty hardware. Most documentation on hardware recommendations for Cassandra is somewhat cryptic and reluctant to put forth any solid numbers on hardware requirements. The Apache Cassandra project documentation[1] has a section titled Hardware Choices, which states:
While Cassandra can be made to run on small servers for testing or development environments (including Raspberry Pis), a minimal production server should have at least 2 cores and 8 GB of RAM. Typical production servers have 8 or more cores and 32 GB of RAM.