Configuration Overview
Mapping involves pairing FC_AL_PA to SCSI target address. The HBA will claim enough SCSI bus entries to allow up to 125 Fibre Channel targets to be mapped to SCSI Bus: Target entries. This is usually done by a fixed mapping of AL_PA to Bus: Target. In such a configuration, the router corresponds to a Bus: Target identifier, with the attached SCSI devices appearing as logical units (LUNs). Operating systems can extend the available SCSI limit of 15 targets per bus. Although this is not an issue for the operating system or most applications, there are cases where older applications can have expectations about what constitutes a valid SCSI ID, and thus may not correctly handle certain mappings. In particular, some applications may exhibit difficulties addressing target IDs greater than 15 (for example, 16 and up). This situation can be resolved by configuring the router to use hard addressing and setting the AL_PA to a value less then 16 that the HBA will be able to map.
For example, depending on the Fibre Channel HBA, if the hard AL_PA selection is 1, then the address is 1. If the selection is 125, the AL_PA address is 0xEF. Some Fibre Channel HBAs will map devices differently, so verify the AL_PA by reviewing the documentation for the HBA.
For more information on AL_PA configuration, see Chapter 3, "Fibre Channel Port Configuration," when using the Visual Manager User Interface or Chapter 4, "Fibre Channel Configuration," when using Serial/Telnet.
Logical Unit Management
Because SAN resources can be shared, it is possible for multiple hosts to have access to the same devices on the SAN. To prevent conflicts, the router provides LUN management as a means to restrict device access to certain hosts. LUN management goes beyond simple LUN masking, to prevent gaps in the list of LUNs presented to a host.
LUN management maps can be created for different views of the devices attached to the router. Each Fibre Channel host is assigned a specific map configuration. Not only can the administrator control which devices a host may access, but also which LUNs are used to access these devices.
For a Fibre Channel host, a map is a table of LUNs, where each entry is either empty or contains device address information needed for host/device communication.
For a SCSI host, a map contains a list of target IDs, each of which has its own table of LUNs with address information needed for host/device communication.
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