HP 418800-B21 Redundancy in enterprise storage networks using dual domain SAS - Page 13

Backplane The same keyed connection layout is applied to system backplanes allowing them to accept both SAS and SATA drives (Figure B-3). Figure B-3. Common backplane for Serial drives One backplane accommodates both SAS and SATA drives... System Backplane SAS Drives SATA Drives Devices The following devices make up dual-domain SAS networks. They also fulfill requirements for switching and data flow over the available paths. Drives and controllers Controllers, HBAs and hard drives (SAS drives) all require dual-ports to have a dual-domain configuration. SATA drives can act as dual-port devices with the intervention of appropriate port selectors or switches. Expander An expander is a device used to facilitate communication among large numbers of SAS devices. Expanders contain two or more external expander ports. Each expander device contains at least one SAS Management Protocol target port for management and may contain SAS devices. For example, an expander may include a Serial SCSI Protocol target port for access to a peripheral device. An expander is not necessary to interface a SAS initiator and target, but a connected expander helps a single initiator communicate with more SAS and SATA targets. By analogy, expanders are like an Ethernet hub in a network that allows connection of multiple systems using a single port in the network. Expanders can be implemented as ASIC (application-specific integrated circuit) components on initiator devices such as an HBA. There are two different types of expanders: Edge Expanders and Fanout Expanders. • An Edge Expander allows the SAS initiator to communicate with up to 128 SAS addresses. • A Fanout Expander can connect up to 128 sets of Edge Expanders, known as an Edge Expander Device Set, to allow addressing even more SAS devices. Cluster Interconnect 13