HP 9124 Serial Attached SCSI storage technology, 2nd Edition - Page 14
Zoning
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Multi-node clusters A multi-node cluster using SAS provides an alternative to clustered Fibre Channel local loop topologies. This highly scalable SAS architecture enables topologies that provide high performance and high availability with no single point of failure. Figure 12 shows a multi-node cluster application using a SAS RAID HBA controller. This SAS topology can also be implemented using an ASIC (application-specific integrated circuit) embedded on the motherboard. Figure 12. Topologies for multi-node cluster applications using a SAS RAID controller provide high performance and high availability. Zoning The number of devices (initiators, targets, expanders, and/or virtual devices) allowed in a given domain is limited only by the size of the expander routing tables. But managing such a large number of devices can be very complicated. Therefore, zoning was introduced into the SAS-2 standard for efficiency (traffic management) and security. With SAS-2, large physical topologies can be broken into logical groups. This grouping allows access within and between zone groups being controlled. A group of zoning-enabled expanders that cooperate to control access between phys is known as a zoned portion of a service delivery system (ZPSDS). There can be 128 or 256 zone groups numbered from 0 to 127 or 0 to 255, respectively. Zone groups 0 through 8 are pre-defined and cannot be changed by the user. Devices in zone group 0 can only access devices in zone group 1, while devices in zone group 1 are allowed access to all zone groups. For example, a system administrator can use zone group 0 for a new (unassigned) device that is added to a ZPSDS. At the same time, the administrator can use zone group 1 for topology discovery and zone management. Permission tables in SAS expanders control zoning. This means that an end device does not require any special features to operate within a zoned SAS domain, which makes legacy SAS and SATA devices compatible. An end device in a zone can only ―see‖ other end devices in the domain as permitted by the zoning expander(s). Figure 13 shows a SAS domain with a ZPSDS containing three zoning expanders in addition to one expander device without zoning enabled. 14