HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 84
Principal, Default, Never Principal, Fabric WWN assignment, Domain ID assignment, A domain ID
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Planning Considerations for Fibre Channel Topologies Note that at least one director or switch in a multi-switch fabric needs to be set as Principal or Default. If all the fabric elements are set to Never Principal, all ISLs will segment. If all but one element are set to Never Principal and the element that was Principal goes offline, then all of the other ISLs will segment. Note: HP recommends configuring the switch priority as Default. In the audit log, note that the Principal setting maps to a number code of 1, Default maps to a number code of 254, and Never Principal maps to a number code of 255. Number codes 2 through 253 are not used. ■ Fabric WWN assignment - The Fabric Manager application identifies fabrics using a fabric WWN. The fabric WWN is the same as the WWN of the fabric's principal switch. If a new principal switch is selected because of a change to the fabric topology, the fabric WWN changes to the WWN of the newly selected principal switch. ■ Domain ID assignment - Each director or switch in a multi-switch fabric is identified by a unique domain ID that ranges between 1 and 31. A domain ID of 0 is invalid. Numerical domain IDs specified by a user are converted to hexadecimal format and are used in 24-bit Fibre Channel addresses that uniquely identify source and destination ports in a fabric. Each fabric element is configured through the Product Manager application with a preferred domain ID. When a director or switch powers on and comes online, it requests a domain ID from the fabric's principal switch (indicating its preferred value as part of the request). If the requested domain ID is not allocated to the fabric, the domain ID is assigned to the requesting director or switch. If the requested domain ID is already allocated, an unused domain ID is assigned. If two operational fabrics join, they determine if any domain ID conflicts exist between the fabrics. If one or more conflicts exist, the interconnecting ISL E_Ports segment to prevent the fabrics from joining. To prevent this problem, HP recommends that all directors and switches be assigned a unique preferred domain ID. This is particularly important if zoning is implemented through port number (and by default domain ID) rather that WWN. 84 SAN High Availability Planning Guide