Fibre Channel

Fibre Channel is a standard interface in the area of the storage area networks. The abbreviation of the associated protocol is FC -P.

Overview

Fibre Channel has been designed for serial, continuous high- speed transmission of large amounts of data.

Many storage area networks today is based on the implementation of the Fibre Channel standards. The achieved data transfer rates are today at 2, 4, 8 and 16 Gbit / s, which is sufficient in full- duplex mode for data transfer rates of up to 1.6 GB / s. However, lower data transfer rates are possible, so until a few years ago 1 Gb / s ( 1GFC ), the maximum data transfer rate in Fibre Channel. The transmission medium is found copper cable (mainly within storage systems, bridges up to 30 m) and fiber optic cable (usually to connect the storage systems among themselves; bridged up to 10 km). Fibre Channel was developed to replace the old SCSI bus. The main use of fiber channel is the transport of SCSI commands, data and status. However, there are many other known upper- layer protocols, such as SNMP, IP or virtual interface.

Similar to traditional networks, where each network card has a MAC address, Fibre Channel, each device has a WWNN (World Wide Node Name ) and each port per device a WWPN (World Wide Port Name ). It is a 64 -bit value (usually represented in hexadecimal ) that uniquely identifies each Fibre Channel device. Fibre Channel devices can have more than one port, in this case the unit is still only a WWNN, but it has WWPNs in the same number as it has ports. The WWNN and WWPN are very similar in general.

The expansion cards that enable the servers to communicate with Fibre Channel, are used as host bus adapters (short: HBA) respectively. Typical HBAs use a PCI Express slot, had older HBAs PCI -X slot with 64 -bit bus width and at least 100 MHz clock rate.

The payload ( de facto data ) of FC frames of up to 2112 bytes of protocol overhead is only 36 bytes (see iSCSI, TCP / IP without Jumbo frames: 1460 bytes Bytes/76, with Jumbo Frames 8960 bytes / 76 bytes). It is used for addressing and integrity checking of the data and is composed of:

  • Start of frame, 4 bytes: marks the beginning of the data block
  • FC frame header, 24 bytes: contains metadata about the block
  • CRC, 4 bytes: checksum to check data integrity
  • End of frame, 4 byte: indicates the end of the data block

Topologies

It can be generally distinguished three types of Fibre Channel topologies:

  • Point To Point (FC- P2P), the simplest implementation, the two ports are connected directly to each other and thus only these two can communicate.
  • Arbitrated Loop (FC- AL), in which up to 127 ports on a ring ( or loop ) are joined together. The addition or removal of a port is the interruption of the entire ring and there may be only one port pair communicate with each other simultaneously. Even if such a ring would be only two ports, the differences in the log significantly in comparison with an FC P2P implementation would. This topology is most comparable to a Token Ring network. FC -AL is also known as low-cost Fibre Channel, it often is the entry into the world of Storage Area Networks. Frequently one finds FC -AL implementations with smaller clusters in which there is more physical nodes possible to directly access a shared mass storage. Here SCSI has reached its limit, which is why one uses the property of the Fibre Channel, which allows to connect multiple hosts with multiple storage subsystems. In this case, all devices available data transmission rate share (depending on the technology used 133 MBit / s to 4 Gb / s ) of the one, available bus. The cascading of the devices are also called Daisy Chain. If a Fibre Channel hub in the game, the wiring is usually star-shaped, although the stroke still produces here a ring topology, in which, however, a failed port no longer silent lays out the entire ring (Port Bypass Circuit). In a FC -AL, the N_Port Report on the Extended Link Service Port Login ( PLOGI ) to.
  • Switched Fabric (FC -SW), wherein up to 224 ports can communicate via Fibre Channel switches together, similar to a modern Ethernet infrastructure. In addition, here many port pairs communicate with each other simultaneously. In the Fibre Channel Switched Fabric is the most powerful and ausfallsicherste implementation of Fibre Channel. In most cases, a switched fabric is meant when it is only spoken by Fibre Channel. In the center of the switched fabric is the Fibre Channel switch or director. This device, all other devices are connected together so that it is possible via the fiber channel switch to connect a direct point-to- point connections between any two attached devices. In order to increase the data transfer rate, it is further possible to incorporate multiple HBAs in a server. After each N_Port HBA of the server with a Fabric Login ( FLOGI ), containing its WWPN and WWNN, has logged on to the switch, the switch registers the host on the local name server with the WWPN / WWNN and a unique address consisting of DomainID ( unique address of the switches in the fabric (see below) ), the port on the server, followed by 00 for switched fabric. This 6-byte address is used for addressing of the ports in the fabric. Moreover, these can be combined with each other ( Fabric) when using multiple switches. The switches then recognize each other the topology and use it intelligently. So the least loaded path is always used ( FSPF - Fabric Shortest Path First ). If the server has more than one HBA has, and each HBA has been inserted on a different switch, the server can thus achieve a storage subsystem in a number of ways. This ability in Fibre Channel is referred to as multi-pathing. It increases the reliability and performance of storage area networks ( SAN), as there is more than one possible data path between devices. To increase the reliability further, one is in many Fibre Channel implementations gone over to work with dual redundant fabric. So there are two completely independent Switched Fabrics operated, each storage subsystem and each server is connected with at least one HBA to each of the two fabrics. The overall system can in addition to the failure of individual data paths to cope with even the failure of a whole fabric, as there is no single point of failure more. This ability plays an important role, particularly in the area of ​​high availability.

Layer

Fibre Channel protocol stack, as well as the OSI and TCP / IP model, divided into layers. Unlike these two, there are five layers ( layers) that can be mapped compared as follows:

FC -2 ( Network Layer ): FC Core

FC -2 ( Network Layer ): FC Core

FC -0 ( Physical): cables, connectors, ...

  • FC -4 - In the Protocol mapping layers are application protocols, such as SCSI or IP packaged into a Protocol Data Unit so that it can be delivered via the FC -2 Layer.
  • FC -3 - advanced features such as RAID protection or encryption can be implemented through the Common Services Layer.
  • FC-2 - The Network Layer. Defined in FC -PI -2 standard, it represents the very core of the FC protocol
  • FC-1 - The Data Link Layer in the implementation of the data line signals is implemented.
  • FC -0 - The Physical Layer, the cabling, connectors and connector types, etc. defined.

The layers FC -0, FC-1 and FC-2 can be grouped under the designation FC -PH as the physical layers of the Fibre Channel.

Fibre Channel router work way up to the FC -4 layer (ie, for example, can act as SCSI routers), switches to FC- 2 and hubs only on layer FC -0.

Fibre Channel products out there and gave it to the speed characteristics 1, 2, 4, 8, 10, 16 and 20 Gbit / s The 16 Gbit / s standard was released in 2010 by the INCITS T11 committee. FC products are only two generations backwards compatible, ie a 4 Gb / s HBA also dominates 2 and 1 Gbit / s, while, however, an 8 Gb / s adapter no longer supports a 1 Gb / s FC infrastructure. The 10 and 20 Gbit / s standards are special cases. They are backwards compatible to any other FC standard and are used practically exclusively for Inter-Switch -Link communication.

Port types in the fabric

Cable lengths

Glass fiber types

Similar standards

  • ATA over Ethernet: For ATA over Ethernet ( ATAoE ) are encapsulated ATA / ATAPI packets into Ethernet. Similar to FC ATAoE is not encapsulated in TCP / IP, ATAoE is therefore also not routable.
  • ISCSI ( SCSI over IP): With iSCSI, SCSI packets are encapsulated in TCP / IP. This results in a higher overhead, but this is iSCSI routable and can be as Fibre Channel over IP, used in wide area networks.
  • HyperSCSI In HyperSCSI SCSI packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to slight performance benefits, but HyperSCSI is not routable.
Ethernet hub Multipath I/O Encapsulation (networking) LIO
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