Much of Cassandra's power lies in the fact that it is a distributed database: rather than storing all of your data on a single machine, it is designed to distribute data across multiple machines. A distributed architecture is hugely beneficial for scalability, since you're not bound by the hardware capacity of a single machine; if you need more storage or more processing power, you can simply add more nodes to your Cassandra cluster. It's also a boon for availability: by storing multiple copies of your data on multiple machines, Cassandra is resilient to the failure of a particular node.
The beauty of a distributed database such as Cassandra is that, as application developers, we rarely need to think about the fact that we're working with data that's spread across multiple servers. We've spent the last nine chapters exploring a wide range of Cassandra's functionality, and the interfaces we've worked with never require us to explicitly account for...