FCP 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. For information about enabling the fcp license, see Managing the FCP service.
In an FCP network, nodes include targets, initiators, and switches. Targets are storage systems, and initiators are hosts. Storage systems have storage devices, which are referred to as LUNs. Nodes register with the Fabric Name Server when they are connected to a Fibre Channel switch.
From the storage system, a LUN is a logical representation of a physical unit of storage. It is a collection of, or a part of, physical or virtual disks configured as a single disk. When you create a LUN, it is automatically striped across many physical disks. Data ONTAP manages LUNs at the block level, so it cannot interpret the file system or the data in a LUN. From the host, LUNs appear as local disks on the host that you can format and manage to store data.
A LUN serial number is a unique 12-byte, ASCII string generated by the storage system. Many multipathing software packages use this serial number to identify redundant paths to the same LUN. You can display the LUN serial number with the lun show -v command.
Storage systems and hosts have Host Bus Adapters (HBAs) so they can be connected directly to each other or to Fibre Channel switches with optical cable. 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 Fibre Channel storage area network (FC SAN), it registers each of its ports with the switch's Fabric Name Server service, using a unique identifier.
Each FCP node is identified by a worldwide node name (WWNN) and a worldwide port name (WWPN).
WWPNs identify each port on an HBA. WWPNs are used for the following purposes:
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 create an igroup by specifying a collection of WWPNs of initiators in an FCP network. When you map a LUN on a storage system to an igroup, you 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. For detailed information about mapping LUNs to igroups, see What is required to map a LUN to an igroup.
You can also create portsets to make a LUN visible only on specific target ports. A portset consists of a group of FCP target ports. You bind a portset to an igroup. Any host in the igroup can access the LUNs only by connecting to the target ports in the portset. For detailed information about portsets, see Making LUNs available on specific FCP 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 HBAs and host target IDs. Some operating systems require persistent binding to ensure that the LUN appears at the same target ID on the host.
When the FCP 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, or
sysconfig -v, fcp nodename, or FilerView (click LUNs > FCP > Report) to see the system's WWNN as FC Nodename or nodename or the system's WWPN as FC portname or portname.
Note
The target WWPNs might change if you add or remove HBAs on the storage system.
The storage system also has a unique system serial number that you can view by using the sysconfig command. The system serial number is a unique 7-digit identifier that is assigned when the storage system is manufactured. You cannot modify this serial number. Some multipathing software products use the system serial number together with the LUN serial number to identify a LUN.
To know which WWPNs are associated with a specific host, see the FCP Host Attach Kit documentation for your host. These documents describe commands supplied by the Attach Kit or the vendor of the initiator or methods that show the mapping between the host and its WWPN. For example, for Windows hosts, you use the lputilnt utility, and for UNIX hosts, you use the sanlun command.
You can use the fcp show initiator command or FilerView (click LUNs > Initiator Groups > Manage) to see all of the WWPNs of the FCP initiators that have logged on to the storage system. Data ONTAP displays the WWPN as Portname.
Fibre Channel switches have one WWNN for the device itself, and one WWPN for each of its ports. For example, the following diagram 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.
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
The FCP service is implemented over the target's and initiator's FCP ports. Initiator HBAs can have one or two ports. Depending on the specific model, a storage system can have two types of target ports:
For detailed information about systems with integrated target ports, see Managing the FCP service on systems with onboard ports.
Each target port has a fixed number of resources, or command blocks, for incoming initiator requests. When all the command blocks are used, an initiator receives a QFull message on subsequent requests. Data ONTAP enables you to monitor these requests and manage the number of command blocks available for specified initiators. You can limit the command blocks used by the initiators in an igroup, or you can reserve a pool of command blocks for the exclusive use of initiators in an igroup. This is known as igroup throttling. For information about igroup throttling, see Managing Fibre Channel initiator requests.
Clustered storage systems in a Fibre Channel SAN require that the following options are enabled to guarantee that takeover and giveback occur quickly enough so that they do not interfere with host requests to the LUNs. These options are automatically enabled (value set to on) when the FCP service is turned on. Do not change them.
If your storage systems are in a cluster, Data ONTAP provides multiple modes of operation required to support homogeneous and heterogeneous host operating systems. The FCP cfmode setting controls how the target ports:
For detailed information, see Chapter 8, Managing FCP in a clustered environment.
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Part No. 210-01094_B0
File: c3ov-f2.htm
Last updated: 08-Dec-2005 13:25:24