Computer hardware and software for providing virtualized access to input/output (I/O) subsystems, for allowing multiple stand-alone application servers or virtual servers to share one or more I/O subsystems, for managing I/O access through one or more virtual I/O servers, for creating a virtual I/O server that includes a multiplexer and associated modules that connect application servers over an I/O switch fabric with one or more Host Bus Adapter (HBA) and/or Network Interface Controllers (NICs), for allowing an application server and the storage and networking resources available from the virtual I/O server to appear as locally attached physical resources (such as NICs and HBAs) to the operating system of the application server, for consolidating I/O access, for allowing multiple servers to share one or more HBAs and NICs, for dynamic control over network and storage I/O bandwidth, for provisioning of network and storage I/O access across multiple application servers, for provisioning of operating systems and applications across multiple application servers, and for controlling high availability and failover for application servers and virtual I/O servers