HP 418800-B21 Redundancy in enterprise storage networks using dual domain SAS - Page 10

phy phy is a generic electronics term referring to an electronic integrated circuit or a functional block of a circuit that encodes and decodes transmissions between a pure digital domain (on-off) and a modulation in the analog domain. A 'SAS phy' is a combination of the physical layer, phy layer and link layer functions. A minimum of two phys (one at the initiator, the other at the target) is required to complete a SAS physical connection pathway, as shown in Figure A-1. Figure A-1. phys are required to complete a SAS physical connection device pPPooorrtrtt pPPhhhyyy link layer SAS phy phy layer physical layer SAS phy physical layer phy layer link layer SAS domain A SAS domain consists of one or more SAS devices and expander devices and can be contained within a SCSI domain SCSI domain A SCSI domain contains a service delivery subsystem and one or more SCSI devices. Additionally, this domain contains a set of SCSI initiator ports and target ports that can communicate with each other when interconnected by a service delivery subsystem. SCSI initiator The SCSI initiator is the host-side endpoint of a SCSI session. SCSI initiators request data transfers from SCSI targets. An HBA is an example of a SCSI initiator. SCSI initiator port A SCSI initiator port acts as the connection between application clients and the service delivery subsystem through which requests and responses are routed. In all cases when this term is used it refers to an initiator port or a SCSI target/initiator port operating as a SCSI initiator port. SCSI target port A SCSI target port contains a task router. It acts as the connection between device servers and task managers and the service delivery subsystem through which requests and responses are routed. When this term is used it refers to a SCSI target port or a SCSI target/initiator port operating as a SCSI target port. 10