Previously, the only option used to be connecting external arrays of disks to CPU over a storage area network. This is still useful today for many customers and remains to be the foundation for a number of their applications.
However, several technology trends and advancements are providing a new option. Virtualization and software-defined storage can abstract compute and storage functions from the underlying hardware. At the same time, CPU and storage are getting more dense, and we also now have high speed networks to connect all of these components together.
When you combine these technologies you get hyper-converged infrastructure, which integrates compute, software defined storage, networking, and virtualization into a single build block for the data center. It enables compute, storage, and networking functions to be decoupled from the underlying infrastructure and run on a common set of physical resources that are based on industry-standard x86 components.
This eliminates the need for a physical SAN components, and by using fast networks to connect them all, we now have the ability to create a true software-defined infrastructure that is connected over a virtual SAN.