Adaptec 3405 User Guide - Page 80

Appendix A: Introduction to SAS ● 80 Some backplanes support daisy-chain expansion to other backplanes. For example, you can daisy-chain (connect one to the next) up to nine Adaptec S50 enclosures to a single SAS card in a host system. SAS Expander Connections A SAS expander device literally expands the number of end devices that you can connect together. Expander devices, typically embedded into a system backplane (see page 79), support large configurations of SAS end devices, including SAS cards and SAS and SATA disk drives. With expander devices, you can build large and complex storage topologies. There are two types of SAS expanders: fanout expanders and edge expanders. Each performs a different role in a storage system. (For more information about how SAS expanders work, refer to the STA Web site at www.scsita.org.) You can connect up to 128 SAS ports to an edge expander. (A single edge expander can therefore support up to 128 SAS addresses.) You can connect up to 128 edge expanders to a fanout expander. You can use only one fanout expander in any single SAS domain (a topology of SAS-and possibly SATA-end devices and expander devices). A single SAS domain can therefore comprise up to 16,384 SAS ports (and therefore up to 16,384 SAS addresses including the fanout expander). The next figure illustrates (in very basic terms) a SAS domain and shows how SAS cards, SAS and SATA disk drives, and expander devices can fit together in a large data storage topology. SAS Domain Disk Drives SAS SAS SATA Disk Drives SATA Disk Drives SATA SAS Edge Expander SATA Disk Drives SATA Edge Expander Edge Expander SAS Card SAS SATA Disk Drives Edge Expander Fanout Expander SAS Card SAS SATA Disk Drives Edge Expander SAS Card SATA Disk Drives SAS