Host bus adapters connect servers to storage networks: Fibre Channel HBAs that give a server its ports into the SAN fabric, SAS adapters that attach external drive shelves, and the converged and high-speed adapters that carry storage traffic in virtualized environments. Every server that boots from or reads a SAN does it through one of these.
Match the HBA to both ends: the server's slot and the fabric's speed and protocol. Port count is a resilience decision as much as a bandwidth one - dual-port adapters and multipath configurations keep storage reachable through a failed link. Check the vendor's compatibility lists for the operating system, the switch fabric, and the storage array, because supported combinations are narrower than the connectors suggest, and keep firmware and driver versions aligned across a cluster. Like-for-like spares shorten the worst day. COLAMCO quotes HBAs with the servers and storage they connect for business, government, and education data centers.