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By Chandan

19th Dec 2011

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FC Theory

SAN Administration & Labs

SAN Troubleshooting & Labs, Test

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Fiber Channel Theory

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It is a dedicated storage network, designed specifically toconnect storage, backup devices, and servers General-purpose networks, such as LANs and WANs, carry

heavy user communications traffic involving printers, email,and so forth. A SAN is the back-end network that carriesstorage traffic, which provides a clear separation of storage

devices from processing and presentation activities andenables the front-end LAN to carry normal TCP/IP traffic SANs have become almost synonymous with Fibre Channel.

However, Fibre Channel is not a required component,because almost any networking or serial SCSI technology canbe

used to create a SAN In addition, the Fibre Channel protocol is designed to carry

not just SCSI traffic, but also TCP/IP traffic and otherprotocols

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Customized physical storage topologiesSANs enable you to establish different physical storage

topologies, which can be customized for the existing business

need, and can readily accommodate change

Reduced costs and easier management of capital assets

SAN connectivity enables storage for many servers to be

consolidated on a small number of shared storage devices,

reducing costs and easing management of capital assets

Cost Effective ExpansionA SAN can be cost-effectively expanded to support more

users, more raw storage, more storage devices, more parallel

data paths, and more widely distributed user populations

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Any-to-any connectivityAny server can potentially talk to any storage device, and

communication among storage and SAN devices (switches,

hubs, routers, bridges) is enabled

Open systems

SANs support multiple operating systems and servers

Centralized management

Using the fast performance, high reliability, and long

distance capabilities of fiber optics, SANs make it practical to

locate the storage systems away from the servers. This opensthe door to storage clustering, data sharing and disaster

planning applications

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High-speed backup

The amount of data being stored, the speed of access to that

data, and the amount of time that data is kept online are all

growing exponentially. Backup and recovery operations are

coming under increasing pressure from collapsing backupwindows and growing storage requirements

Because SANs remove backup and recovery traffic from the

LAN, congestion is reduced and backup windows are

improved. System performance is dramatically increasedbecause data and communications traffic no longer compete

for the limited bandwidth on a standard LAN

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Serverless Backup SANs also can be configured for serverless (active fabric)

backup. Serverless backups use the Network DataManagement Protocol (NDMP), the standard for backing upnetwork-attached storage, and SCSI Extended Copy to movethe data directly from disk to tape. This enables continuous,

uninterrupted access to data and applications during thebackup and restore processes

This technology also eliminates the read/write processesthrough the application and backup hosts, resulting in up to97% less processing power. By removing the LAN, CPU andI/O resources from the data path, network bottlenecks areeliminated and high application performance is maintained

Serverless backup is ideal for large databases or file serversfor which there is no backup window

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Why Fibre Channel?

Fibre Channel layers and their components &

Functionality

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A standard: AN ANSI standard providing flexible serialdata transport at long distances for Storage Area andSystem Area Networks - ratified as ANSI standard in1994. Now an ISO/IEC Standard

High performance and speed: Hardware based transportmechanism for high performance; 1, 2, 4, 10 Gb/s speeds

Low latency: Less than 2 micro second latency input portto output port of FC switch

Long distance: Up to 10KM distance (longer withextenders), can be extended non-natively over ATMs upto 3000 km

Robust data integrity: Uses IBMs 8B/10B encodingscheme for robust integrity plus FC has a bit error rate(BER) of 10-12 - about 1 bit error every trillion bits.

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Large connectivity: Per the standard, Fibre Channel allows a theoretical 16M

devices to be connected to one Fabric Support for multiple physical media types - Copper, Optical

Fibre (multimode and Single mode) and Mixed media

Support for multiple protocols - SCSI, IP, VIA, FICON, etc.and mixed protocols Support for multiple topologies - Point-to-Point, Switched,

Loop and mixed topologies Heterogeneous interconnect scheme for computing and

peripheral devices

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To prevent a target device from being overwhelmedwith frames, Fibre Channel provides several flow controlmechanisms based on a system of credits. Each creditrepresents a device's ability to accept an additionalframe. If the recipient issues no credits to the sender,no frames can be sent. Pacing frame transport on the

basis of credits prevents loss of frames and reduces thefrequency of entire sequences being retransmittedacross the link

There are two Types of Flow control Mechanisms1. End-to-end flow control2. Buffer-to-buffer credit (BB_Credit)

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Transmission credit is initially established when two communicating

nodes log in and exchange communication parameters. End-to-endflow control (EE_Credit) is used by Class 1 and Class 2 servicebetween two end nodes and is monitored by the nodes themselves.An intervening switch does not participate in EE_Credit. After an initialcredit level is granted, credits are replenished by acknowledgmentsissued by the receiver to the sender. The sender decrements theEE_Credit by 1 for each frame issued and increments only when anACK is received.

Buffer-to-buffer credit (BB_Credit) is used by Class 2 and Class 3service and relies on the receiver-ready (R_RDY) ordered set toreplenish credits. An end node attached to a switch will establish itsBB_Credit during login to the fabric. A communicating partner on thefar side of the switch will establish its own (and possibly different)BB_Credit to the switch during login. BB_Credit thus has no end-to-end component. The sender decrements the BB_Credit by 1 for eachframe sent, and increments BB_Credit by 1 for each R_RDY received.The initial value of the BB_Credit must be nonzero.

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Objectives:

Fibre Channel Topologies

FC Addressing

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Switch Initialization Device initialization

What happens when a Fabric device connects to a

Fabric?

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