Free Tutors On In-band management in Fibre Channel SAN Discovery, Massages and Monitoring
The Fibre Channel Methodologies for Interconnects (FC-MI) and Fibre Channel Generic Services 4 (FC-GS-4) standards defined by the American National Standards Institute (ANSI) form the basis for the in-band management in the Fibre Channel SAN. The FC-MI standard describes general methods to guarantee interoperability between various devices. In particular, this defines the prerequisites that a device must fulfil for in-band management. The FC-GS-4 standard defines management services that are made
available over the so-called Common Transport Interface of the Fibre Channel protocol. Services for management There are two Fibre Channel services that are important to Fibre Channel SAN management: the directory service and the management service. Each service defines one or more so-called servers. In general, these servers – split into individual components – are implemented in distributed form via the individual connection nodes of a Fibre Channel SAN but are available as one single logical unit. If an individual component cannot answer a management query, then the query is forwarded to a different server component on a
different node. This implementation is comparable to the Domain Name Services (DNS) that we know from IP networks.
The Fibre Channel standard defines, amongst other things, the following servers that are of interest for the management of storage networks:
• Name server The name server is defined by the directory service. It is an example of an operational service. Its benefit for a management system is that it reads out connection information and the Fibre Channel specific properties of a port (node name, port type).
• Configuration server The configuration server belongs to the class of management-specific services. It is provided by the management service. It allows a management system to recognize the topology of a Fibre Channel SAN.
• Zone server The zone server performs both an operational and an administrative task. It permits the zones of a Fibre Channel SAN fabric to be configured (operational) and recognized (management-specific). These services make it possible for a management system to recognize and configure the devices, the topology and the zones of the SAN.
Discovery
The configuration server is used to identify devices in the Fibre Channel SAN and to recognize the topology. The so-called RNID function (Request Node Identification Data) is also available to the management agent via its host bus adapter API, which it can use to request identification information from a device in the Fibre Channel SAN. The RTIN function (Request Topology INformation) allows information to be called up about connected devices. Suitable chaining of these two functions finally permits a management system to rec- ognize the entire topology of the Fibre Channel SAN and to identify all devices and properties. If, for example, a device is also reachable out-band via a LAN connection, then its IP address can be requested in-band in the form of a so-called management address. This can then be used by the software for subsequent out-band management.
Monitoring
Since in-band access always facilitates communication with each node in a Fibre Channel SAN, it is simple to also request link and port state information. Performance data can also be determined in this manner. For example, a management agent can send a request to a node in the Fibre Channel SAN so that this transmits its counters for error, retry and traffic. With the aid of this information, the performance and usage profile of the Fibre Channel SAN can be derived. This type of monitoring requires no additional management entity on the nodes in question and also requires no out-band access to them. The FC-GS-4 standard also defined extended functions that make it possible to call up state information and error statistics of other nodes. Two commands that realize the collection of port statistics are: RPS (Read Port Status Block) and RLS (Read Link Status Block).
Messages
In addition to the passive management functions described above, the Fibre Channel protocol also possesses active mechanisms such as the sending of messages, so-called events. Events are sent via the storage network in order to notify the other nodes of status changes of an individual node or a link. Thus, for example, in the occurrence of the failure of a link at a switch, a so-called
Registered State Change Notification (RSCN) is sent as an event to all nodes that have registered for this service. This event can be received by a registered management agent and then transmitted to the management system.
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