Fibre Channel
This chapter provides a high level overview of the Fibre Channel (FC) protocol.
The following topics are covered:
26.1 Fibre Channel defined
First started in 1988 and got ANSI standard approval in 1994, Fibre Channel (FC) is now the most common connection type for storage area network (SAN). Nowadays FC SAN is already an indispensable infrastructure component in any current complex IT environment. With the proliferation of various in-house developed and packaged applications supported by various implementations from different infrastructure components, managing modern IT environment is becoming more complicated because everybody is competing with resources and expecting the best service level with minimal unscheduled downtime.
FC is a licensed service on the storage system that enables you to export LUNs and transfer block data to hosts using the SCSI protocol over a Fibre Channel fabric.
26.2 What FC nodes are
In an FC network, nodes include targets, initiators, and switches.
Targets are storage systems, and initiators are hosts. Nodes register with the Fabric Name Server when they are connected to an FC switch.
26.3 How FC target nodes connect to the network
Storage systems and hosts have adapters, so they can be directly connected to each other or to FC switches with optical cables. For switch or storage system management, they might be connected to each other or to TCP/IP switches with Ethernet cable.
When a node is connected to the FC SAN, it registers each of its ports with the switch’s Fabric Name Server service, using a unique identifier.
26.4 How FC nodes are identified
Each FC node is identified by a worldwide node name (WWNN) and a worldwide port name (WWPN).
26.4.1 How WWPNs are used
WWPNs identify each port on an adapter. They are used for creating an initiator group and for uniquely identifying a storage system's HBA target ports.
•Creating an initiator group: The WWPNs of the host’s HBAs are used to create an initiator group (igroup). An igroup is used to control host access to specific LUNs. You can create an igroup by specifying a collection of WWPNs of initiators in an FC network. When you map a LUN on a storage system to an igroup, you can grant all the initiators in that group access to that LUN. If a host’s WWPN is not in an igroup that is mapped to a LUN, that host does not have access to the LUN. This means that the LUNs do not appear as disks on that host. You can also create port sets to make a LUN visible only on specific target ports. A port set consists of a group of FC target ports. You can bind an igroup to a port set. Any host in the igroup can access the LUNs only by connecting to the target ports in the port set.
•Uniquely identifying a storage system’s HBA target ports: The storage system’s WWPNs uniquely identify each target port on the system. The host operating system uses the combination of the WWNN and WWPN to identify storage system adapters and host target IDs. Some operating systems require persistent binding to ensure that the LUN appears at the same target ID on the host.
26.4.2 How storage systems are identified
When the FC protocol service is first initialized, it assigns a WWNN to a storage system based on the serial number of its NVRAM adapter. The WWNN is stored on disk.
Each target port on the HBAs installed in the storage system has a unique WWPN. Both the WWNN and the WWPN are a 64-bit address represented in the following format: nn:nn:nn:nn:nn:nn:nn:nn, where n represents a hexadecimal value.
You can use commands such as fcp show adapter, fcp config, sysconfig -v, or
fcp nodename to see the system’s WWNN as FC Nodename or nodename, or the system’s WWPN as FC portname or portname.
fcp nodename to see the system’s WWNN as FC Nodename or nodename, or the system’s WWPN as FC portname or portname.
26.4.3 How hosts are identified
You can use the fcp show initiator command to see all of the WWPNs, and any associated aliases, of the FC initiators that have logged on to the storage system. Data ONTAP displays the WWPN as Portname.
To know which WWPNs are associated with a specific host, see the FC Host Utilities documentation for your host. These documents describe commands supplied by the Host Utilities or the vendor of the initiator, or methods that show the mapping between the host and its WWPN. For example, for Windows hosts, you must use the LightPulse utility (lputilnt), HBAnyware, or SANsurfer applications, and for UNIX hosts, you must use the sanlun command.
26.4.4 How switches are identified
Fibre Channel switches have one worldwide node name (WWNN) for the device itself, and one worldwide port name (WWPN) for each of its ports.
For example, Figure 26-1 shows how the WWPNs are assigned to each of the ports on a 16-port Brocade switch. For details about how the ports are numbered for a particular switch, see the vendor-supplied documentation for that switch.
Figure 26-1 Sample switch WWNN
Port 0, WWPN 20:00:00:60:69:51:06:b4
Port 1, WWPN 20:01:00:60:69:51:06:b4
...
Port 14, WWPN 20:0e:00:60:69:51:06:b4
Port 15, WWPN 20:0f:00:60:69:51:06:b4
Port 1, WWPN 20:01:00:60:69:51:06:b4
...
Port 14, WWPN 20:0e:00:60:69:51:06:b4
Port 15, WWPN 20:0f:00:60:69:51:06:b4
26.5 Further information
More details on SAN and the Fibre Channel protocol can be found in the following Redbooks publications:
•Designing an IBM Storage Area Network, SG24-5758, located at this website:
•Introduction to Storage Area Networks and System Networking, SG24-5470,
located at this website:
located at this website:
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