Intro to Fibre Channel

7/30/2019 Intro to Fibre Channel

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This course presents the student with the necessary information to understandthe basics of Fibre Channel protocol, Fibre Channel topologies, WWN usage,and Fibre Channel logins in a SAN or NAS environment.

Upon completion of this course, you will be able to:

Discuss basics of Fibre Channel protocol

Identify differences between the Fibre Channel topologies

Identify three types of Fibre Channel logins and their functions

Define WWN and discuss its role in Fibre Channel environments

Introduction to Fibre Channel

Fibre Channel is a connectivity technology designed totransmit data between devices, commonly in a storage area

network. The objectives covered in this module are: Explain the role of Fibre Channel as a transmission interface

List the Fibre Channel levels and discuss each level

Identify characteristics of Fibre Channel transmission media

Fibre Channel Overview


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Fibre Channel extends networking concepts to storage, including distance,speed, connectivity, scalability, and reconfiguration. The Fibre Channeltechnology provides for improved data transfer rates and greater distancesthan traditional Small Computer System Interface (SCSI) cable. Uponcompletion of this lesson, you will be able to:

Define Fibre Channel and describe its use in a storage area network

Compare and contrast Fibre Channel and SCSI

Identify EMC products that use Fibre Channel connectivity

Fundamentals

Fibre Channel is a serial data transfer interface that operates over copper wire and optical fiber. Fibre Channel solves manyproblems associated with input/output (I/O) interfaces and interconnections among systems in an environment.

Definition and Use


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Simultaneous communication among hosts, servers, storage systems and other devices is possible through Fibre Channeltechnology, using SCSI, IP, and other protocols. This interconnection is available for different topologies, providing reliability andhigh bandwidth.

Performance Impact

Products associated with an Enterprise Storage Network facilitate fast, reliable interconnects, including switches, hubs, adaptersand storage arrays.

Associated Products


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The Fibre Channel Physical and Signaling standard, ANSI, and ISO specify standards for Fibre Channel. A Standard is a set ofdocuments that is widely recognized and employed, defining the set of rules and configurations of a product or practice. AllStandards are subject to revision, and all parties are subject to agreements based on a Standard.

Standards

The Fibre Channel alliance determines the standards for the Fibre Channel protocol. Protocol standards can be obtained by goingto www.t11.org.

Protocol Standards


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The first generation of storage was connected using SCSI. By adding an external SCSI connection from a host to a storage system,the amount of storage was drastically increased. Certain conditions and limitations were imposed on this configuration, based onthe SCSI standards.

Comparison to SCSI

Replacing the hardwired standard SCSI cable with fiber cable in a Fibre Channel environment resulted in an increase in both thedistance between a host system and a storage system, and the throughput.

Increased Distance and Throughput


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Networking and I/O protocols such as SCSI commands are mapped to Fibre Channel constructs, then encapsulated andtransported within Fibre Channel frames. This allows the SCSI protocol to be used over a Fibre Channel network.

Protocols Mapped

Fibre Channel is designed to provide throughput that is not protocol dependent. It allows a consolidation of storage systems andhardware such as cables and connectors.

Benefit of Single Technology


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Traditionally, SCSI has been used as an I/O interface, utilizing bus-oriented interconnection. Today we see the emergence of IP asanother possible protocol that could be enhanced by being used with Fibre Channel. It is possible to have several Upper LevelProtocols (ULP) transmitted within a Fibre Channel environment, simplifying the physical layout of a storage area network.

Internet Protocol

EMC offers a series of Fibre Channel devices and services. Among these offerings is the Connectrix Family of Switches.Connectrix switches are generally divided into two categories: M-Series and B-Series.

Fibre Channel and EMC Products, Services, and Offerings


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Management tools are available for each type of switch. EMC ESN Manager is a consolidated tool for managing zoning and volumeaccess on switches and directors. Each switch series also has a native management tool that provides its own flexible scheme forzoning management and switch management applications, including Connectrix Manager for the M-Series switches, and web andtelnet-based management tools for B-Series switches.

Management Software

EMC offers Fibre Channel connectivity to its storage systems: Symmetrix and CLARiiON.

Storage Systems


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Fibre Channel provides protocol independent distance, throughput, and speed that is superior to the capabilities of SCSI. EMCprovides fibre channel connectivity to storage arrays through the Connectrix family of switches and storage systems.

Lesson Summary

Fibre Channel Topologies


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The Fibre Channel Architecture has been designed in levels to allow formanageability and future growth. Fibre channel levels can be compared tothe ISO/OSI 7-layer model in that it attempts to define the different aspectsof Fibre Channel in manageable pieces. However all five levels of FibreChannel would fit within the first three layers of the 7-layer model, and therouting capabilities of Fibre Channel are limited. Upon completion of thislesson, you will be able to:

Describe attributes of FC-0, FC-1, and FC-2

Identify the roles of FC-3 and FC-4 in Fibre Channel protocol

Fibre Channel Levels

The Fibre Channel Architecture has been designed in levels to allow for manageability and future growth. Similar to the ISO/OSI 7-Layer model, any of the levels could be updated or modified without impact to the other levels.

Designed for Flexibility


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FC-0 is the lowest level and defines the physical link in the system, including the fibre, connectors, optical and electricalcomponents. This level covers a variety of media and the associated drivers and receivers capable of operating at a wide range ofspeeds.

FC-0

Each fibre cable is attached to a transmitter of a port at one end and a receiver of another port at the other end. When a fabric ispresent in the configuration, a fibre cable may attach between an N_Port and an F_Port. In an Arbitrated Loop, the cable attachesbetween NL_Ports. Other devices may be present and function as repeaters, concentrators or fibre converters.

Fibre and Port Attachment


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Optical and Electrical connectors are specified in Fibre Channel. The SC connector is the standard connector for fiber optic cables.It is a push-pull connector and is favored over the ST connector. If the cable is pulled, the tip of the cable in the connector does notretract, which would result in loss of signal quality.

Connectors

Multimode cable is dominant for short distances of 500 meters or less. Multimode has an inner diameter of 62.5 or 50 microns,allowing light to enter the cable in multiple modes, including straight and at different angles. The many light beams tend to loseshape as they move down the cable. This loss of shape is called modal dispersion and limits the distance.

Multimode Cable


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Single mode cable is used for long distance cable runs, only limited by the power of the laser at the transmitter and by thesensitivity of the receiver. Single mode cable has an inner diameter of 9 microns and is always used with a long wave laser, whichlimits the effects of modal dispersion. Therefore, with single mode cables the distance is greatly increased.

Single Mode Cable

FC-1 defines the transmission protocol including serial encoding and decoding, special characters and error control. Information isencoded 8 bits at a time into a 10 bit transmission character and transmitted over the cable.

FC-1


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Fibre Channel transmits information using an adaptive 8B/10B code to bound the maximum run length of the code, maintain DC-balance, and provide word alignment. The encoding process results in the generation of Transmission Characters.

Encoding Process

Two types of Transmission Characters (Data and Special) are defined. Certain combinations of Transmission Characters, referredto as Ordered Sets, are designated to have special meaning. Ordered Sets are used to identify frame boundaries, transmit primitivefunction requests, and maintain proper link transmission characteristics during periods of inactivity.

Ordered Sets


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The FC-2 level serves as the transport mechanism of Fibre Channel. The transported data is transparent to FC-2 and visible to FC-3 and above.

FC-2

Frames are the basic building blocks of a Fibre Channel connection. The frames contain the information to be transmitted, theaddress of the source and destination ports and link control information.

Frames


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All information in Fibre Channel is passed in frames. The maximum amount of data carried in a frame is 2112 bytes, total framesize is 2148 bytes. The general structure of a Frame is specific.

Role of Frames

The header contains the Source and Destination Addresses which allows the frame to be routed to the correct port. The Type fieldinterpretation is dependent on whether the frame is a link control frame or a Fibre Channel data frame. For example, if the frame isa data frame, a 08 in the type field would indicate a SCSI FCP information in the Data field.

Header Contents


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An Exchange is a unidirectional or bi-directional set of non-concurrent Sequences. An Exchange is the largest construct understoodby FC-2. FC-2 manages Exchanges that map directly to operations.

Exchange

FC-2 manages Sequences as unidirectional transfers of one or more frames. A Sequence is contained within an Exchange and iscomprised of one or more Frames. FC-2 names each Sequence and tracks each Sequence to completion. The purpose of theSequence is to reorder data when it is received at the other end.

Sequences


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FC-2 provides flow control for buffer management. When nodes initialize on the fabric they agree on operational parameters suchas the number of buffers available (Buffer Credits). Transmitting nodes can continue to transmit as long as there are buffer credits.R_RDY are sent to a transmitting node as buffers are cleared.An FC switch also performs buffering and flow control internally andexternally.

Buffer to Buffer Credit

Classes of Service are different types of topology independent services provided by the Fabric and used by the communicatingN_Ports destination. The allocation and retention method between the N_Ports and the level of delivery integrity required for anapplication distinguish classes of service. If the Fabric is not present, the service is provided as a special case of point-to-point.Fabrics and N_Ports are not required to support all Classes of service.

Classes of Service


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The FC-4 level of Fibre Channel is designed to hand off to another protocol such as SCSI. Fundamentally, the commands at FC-4for SCSI allow SCSI initiator and target to communicate over Fibre Channel. FC-3 level functions are not implemented at this time.

FC-4 and FC-3

FC-3 was put into Fibre Channel as a placeholder. In concept FC-4 would pass requests to FC-3 that would perform the desiredservice and then pass onto FC-2.

Purpose of FC-3


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The FC-4 level consists of several standards documents describing how different upper-level protocols (ULPs) use the transportservices provided by levels FC-2, FC-1 and FC-0. The purpose of an FC-4 protocol mapping is to make a logical connectionbetween the ULPs and Fibre Channel's transport facilities.

Purpose of FC-4

Fibre Channel levels, like the OSI model, are divided into manageable layers that have different functions. FC-0 and FC-1 areconnectivity and transmission based, FC-2 is the transport mechanism and FC-4 connects these levels to ULPs.

Lesson Summary


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Fibre Channel-based enterprise storage networks dramatically increase the number of systems that connect to enterprise storage.The extended distance characteristics of Fibre Channel break through the walls of the data center to let departmental servers anddatabases participate in enterprise storage. The throughput that Fibre Channel provides make connecting hundreds of systems tocentralized enterprise storage possible from a performance standpoint.

Module Summary

Fibre Channel connectivity transmits data in three maintopologies. Fibre Channel frames provide routing information,

and a series of logins allows information to be transmitted.Upon completion of this module, you will be able to:

Differentiate between Arbitrated Loop and Switched Fabrictopologies

Discuss the role of Worldwide Names in Fabric Addressing

Identify the use of fabric, port, and process logins in a fabricenvironment

Using Fibre Channel


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The three basic topologies in Fibre Channel are point-to-point, ArbitratedLoop (FC_AL) , and Switched Fabric (FC-SW). EMC supports FC-AL andFC-SW, and refers to a two node FC-AL as Direct Connect. Uponcompletion of this lesson, you will be able to:

Describe characteristics of Direct Connect topology

Describe characteristics of Arbitrated Loop topology

Describe characteristics of Switched Fabric topology

Fibre Channel Topologies

Nodes are central to any communication between two devices. In general, a node is a point of contact where data enters or leavesa device. An HBA in a host or a fibre port in a storage system can be referred to as a node.

Nodes


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Each node has at least one port that connects to other ports on other nodes.

Node Ports

There are several different port types, including: NL_Port, N_Port, F_Port, and E_Port.

Port Types


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In a direct connect system, the nodes are connected directly to one another. Arbitrated loop can also be used as a method of directconnection in which a hub is used and each node is cabled to the hub.

Direct Connect and Arbitrated Loop

Fibre Channel Arbitrated Loop allows only one pair of nodes to transfer data at a time, and nodes arbitrate for use. EMC requiresthis to be implemented using a FC-AL hub. The hub provides a full bandwidth loop that is shared between the nodes on the loop,however only one virtual circuit can be established at a time.

FC_AL Hub


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The FC-AL architecture will support from 2 to 126 nodes on a private loop. During the loop initialization process (LIP), each node onthe loop is assigned an Arbitrated Loop Physical Address (AL-PA).The nodes in the loop then follow a standard arbitration protocolthat defines the rules for gaining access to the loop.

Private Loop

Loop access priority is based upon the AL-PA of the nodes. At anytime there can be only a single full bandwidth circuit openbetween 2 nodes on the loop.

Loop Access


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EMC specifies a 2 node FC-AL connection called Direct Connect. This Topology is the same as the standard Arbitrated Loopexcept that there are two nodes in the Loop and the FC-AL Hub is not used.

EMC Specification

Direct connect and Arbitrated Loop pose limitations in certain environments.

Limitations


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A direct Fibre Channel direct connect between host and storage array provides greater distance and throughput than SCSI, butallows only a 1:1 port density ratio.

Port Density

Arbitrated loop solves the issue of port density by allowing multiple hosts to access multiple storage systems. However, only onevirtual circuit, thus impacting overall SAN performance at a time is possible between nodes, thus limiting bandwidth in a storagearea network.

Performance Impact


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A Fabric is a switch or switches, managed centrally, and is capable of routing frames by using only the D_ID information in a FC-2frame header. A fabric can be comprised of either a single switch or a multi-switch configuration.

Switched Fabric

In a switched fabric environment, the total network bandwidth is determined by the number of ports on the switch. For instance, an8 port 100MB switch can support up to 800 MB/s aggregate bandwidth.

Dedicated Bandwidth


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A switched fabric allows multiple virtual circuits to transport data at a time, eliminating the bandwidth issues presented by ArbitratedLoop.

Virtual Paths

EMC has defined the maximum number of switches in a Fabric to be 16. Currently this allows over 1024 ports to be available in asingle fabric. This number will increase over time.

Greater Expandability


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Although the price of FC-SW devices is higher than that of FC-AL, the performance and throughput far exceed the capabilities ofFC-AL Hub devices. Additionally, the management and redundancy features of FC-SW devices allow for a very stable, manageableand high-throughput environment.

Price and Performance

The three basic topologies of Fibre Channel are direct connect, arbitrated loop, and switched fabric. Switched fabric provides themost throughput, flexibility, and scalability, allowing the highest number of ports in a single fabric.

Lesson Summary


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SCSI to Fibre Channel

Worldwide Names are assigned to entities including ports. WorldwideNames are assigned by the vendor and do not change. When nodes

generate frames, they are routed by their addresses, not their WWNs. AWorld Wide Name is a 64 bit value (16 characters).Upon completion of thislesson, you will be able to:

Identify the contents of a Fibre Channel frame

State the role of the WWN in a Fibre Channel environment

Identify characteristics of Fibre Channel name formats

Addressing and Worldwide Names


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Fibre Channel addresses are used to designate the source and destination of frames in the Fibre Channel network. The FibreChannel address field is 24 bits /3 bytes in length.

Fibre Channel Addressing

Unlike Ethernet, these addresses are not burned in, but are assigned when the node either enters the loop or is connected to theswitch. There are reserved addresses, which are used for services rather than interface addresses.

Assigned Addresses


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When an N_Port connects to the fabric, the switch assigns and transmits a physical fabric address to the N_Port. This addressbecomes the Source ID (S_ID) on the outbound frames and the Destination ID (D_ID) on the inbound frames.

S_ID and D_ID

Address identifiers are three bytes in length. The Frame Header contains two three-byte fields for address identifiers, the (D_ID)field and the (S_ID) field. Each N_Port has a fabric-unique identifier, the N_Port Identifier, by which it is known. The source anddestination N_Port Identifiers and alias address identifiers are used to route frames within the fabric.

Address Formats


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The Physical address of an N_Port can change, such as when a link is moved from one switch port to another switch port. TheWWN of the N_Port, however, is static.

Address Changes

Worldwide names are assigned by the vendor to all Fibre Channel entities.

Worldwide Name


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Each N_Port attached to a fabric has a World Wide Name. Most HBAs have the WWN "burned in" to the hardware. WWNs can alsobe assigned through software.

WWN Assignment

When nodes generate frames, they are routed by their addresses, not their WWNs. However, tables can be built which canassociate WWNs to the destination addresses. A World Wide Name is a 64 bit value (16 characters).

Routing


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The most significant 8 bits of the Fibre Channel address contain the Domain ID, which basically identifies the switch. In the Fabricenvironment this allows frames to be routed between switches. The middle 8 bits contain the area address, which has beenimplemented as the port address within the switch.

Fabric Environment

Fibre Channel specifications allow for multiple formats of the World Wide Name. The example shown is that of the IEEE RegisteredName Format.

Fibre Channel Name Formats


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The Fibre Channel name is 64 bits in length The first 4 bits identify the format being used. The 5 in this example identifies theformat as IEEE Registered Name Format.

Length of Fibre Channel Name

Values for worldwide name formats are based on the IEEE company_id. More information on these formats can be found atwww.standards.ieee.org.

IEEE company_id


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Fibre Channel protocol uses Worldwide Names to identify entities such as ports. Fibre Channel Addresses are used for routing offrames from their source to their destination.

Lesson Summary

When using Fibre Channel to establish communication, a series of FibreChannel logins are initiated. Upon completion of this lesson, you will be

able to: Identify logins used in a Switched Fabric environment

Identify logins used in Arbitrated Loop environment

Fibre Channel Logins


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The fabric login is specific to Switched Fabric and does not occur in Arbitrated Loop or Direct Connect.

Switched Fabric

An N_Port uses fabric login (FLOGI) to determine the presence of a fabric. The fabric login communicates identities and exchangesservice parameters to establish a session with the fabric. It is also the mechanism by which the fabric assigns an address to anN_Port. A fabric login process begins when the N_Port performs a login (to address FFFFFE) using a source address of 000000.The Fabric Login service returns a frame that assigns a 24-bit address to the port.

Fabric Login Process


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Prior to performing an N_Port Login, the incoming Node should perform a registration with the distributed name service (dNS). Theservice which handles this is called the Directory Server and appears as a normal N_Port with the address of x' FF FF FC'.

Distributed Name Service

Port and Process Logins occur in all Fibre Channel topologies. All relevant logins must occur in order for device discovery to takeplace.

Switched Fabric and Arbitrated Loop


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Loop Initialization is performed to assign an AL_PA to a Node entering a Loop. During the Loop Initialization Process, Primitives aresent to ensure that all Nodes have unique AL_PAs. Nodes previously within the Loop will retain their previous addresses, while newNodes entering may acquire either a Hard or Soft assigned address.

Arbitrated Loop

Once a port has logged in, it can query the Name Service database for information about other logged in ports.

Loop Initialization Process


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Fibre Channel logins are performed between ports prior to initiating higher-level protocol operations. The port login (PLOGI) followsthe fabric login process, allowing two N_Ports to establish a session and exchange identities and service parameters.

Port Login

Port logins exchange information such as host source identification frame, frame size, and Port name; the output refers to thesevalues as host SID, receive buffer size, and WWPN respectively.

Port Login Function


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When an N_Port logs in to another N_Port, tables are built which will keep track of the WWN of the logged-in port along with itsFibre Channel address.

Port Data Table

The process login establishes a session between two FC-4 level processes at different N_Ports, basically performing a bindingbetween two processes.

Process Login


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Once the process login has been performed, the two ports may exchange information that can be used to identify a specific processat the initiator and target ports.

Process Information Exchange

Fabric, port, and process logins allow SCSI device discovery to take place in a switched environment: The fabric login establishes asession with the fabric and assigns an address to an N_Port. The port login follows, allowing two N_Ports to establish a session.The process login then binds two processes, and the two ports may exchange information.

Lesson Summary


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Fibre Channel addressing is determined by the topology used. Addresses are dynamically assigned. The addresses include theDomain, Area, and Port fields. The Domain ID portion of an address identifies the switch. Fibre Channel N_ports are usuallyreferred to by their WWN. Everything, including the fabric itself, in a Fibre Channel environment has a WWN.

Module Summary

Fibre Channel provides a number of benefits to enterprise storage capabilities, including the flexibility of encapsulating and

transporting SCSI commands in fibre channel frames. Each device in a fabric has a node that transports information, such as theHBA on the host, the FA on Symmetrix, and the SP on CLARiiON. Addresses containing source and destination information areassigned when the node logs into the fabric. Node ports are each identified with a unique Worldwide Name. Nodes use a series oflogins based on Fibre Channel protocol. The fabric login is first used to establish a session. The port login allows informationexchange between ports. The process login then binds the two ports.

Course Summary


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Course Conclusion

Documents

Intro to Fibre Channel