HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 96
Fabric Island, Tier 1
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Planning Considerations for Fibre Channel Topologies The simplest core-to edge fabric has two or more core switching elements that may or may not be connected (simple or complex). In a simple core topology, as shown in Figure 39 on page 94, core switches are not connected. In a complex core topology, as shown in Figure 40 on page 95, core switches are connected. The figure also illustrates a topology where the core is a full-mesh fabric. Each edge switch connects (through at least one ISL) to each core switch, but not to other edge switches. There are typically more device connections to an edge switch than ISL connections; therefore, edge switches act as consolidation points for servers and storage devices. The ratio of ISLs to device connections for each switch is a function of device performance. For additional information, refer to "ISL Oversubscription" on page 99. Fibre channel devices (servers and storage devices) connect to core or edge fabric elements in tiers. These tiers are defined as follows: ■ Tier 1 - A Tier 1 device connects directly to a core director or switch. Tier 1 devices are typically high-use or high-I/O devices that consume substantial bandwidth and should not be connected through an ISL. In addition, IBM fiber connection (FICON) devices cannot communicate through E_Ports (ISLs) and must use Tier 1 connectivity. For additional information, refer to "FCP and FICON in a Single Fabric" on page 108. ■ Tier 2 - A Tier 2 device connects to an edge switch and Fibre Channel traffic from the device must traverse only one ISL (hop) to reach a device attached to a core director or switch. ■ Tier 3 - A Tier 3 device connects to an edge switch and Fibre Channel traffic from the device can traverse two ISLs (hops) to reach a device attached to a core director or switch. Fabric Island A fabric island topology connects several geographically diverse Fibre Channel fabrics. These fabrics may also comprise different topologies (cascaded, ring, mesh, or core-to-edge), but may require connectivity for shared data access, resource consolidation, data backup, remote mirroring, or disaster recovery. When connecting multiple fabrics, data traffic patterns and fabric performance requirements must be well known. Fabric island connectivity must adhere to topology limits, including maximum number of fabric elements and ISL hop count. It is also essential to maintain data locality within fabric islands as much as possible, and to closely monitor bandwidth usage between the fabric islands. 96 SAN High Availability Planning Guide