HCI (Hyper-converged infrastructure) is a software-defined IT infrastructure that virtualizes all of the elements of conventional "hardware-defined" systems. HCI includes virtualized computing (a hypervisor), software-defined storage and virtualized networking.
Traditionally, SAN storage is essential for shared storage between servers. HCI eliminate the need for SAN. Software-defined storage of HCI manage storage disperse in HCI nodes as centralized storage. HCI is this more affordable than buying physical servers and SAN. HCI is also more expandable by introduce more nodes to the HCI.