Modeling and Evaluation of Fibre Channel Storage Area

Networks

Xavier Molero, Federico Silla, Vicente Santonia and Jose Duato

Introduction

What is a SAN (Storage Area Network)A separate high-speed network for storage Isolated from messaging networkOptimized for moving data between

servers and storage devices

How it is different from traditional server-storage network

Traditional Server-Storage Architecture

Limitations:Unavailability of data in case of a failure on serverBandwidth saturation during backups

Typical SAN Architecture

Fibre Channel

Generic transport mechanismProvides an interface for high-speed data transfer(gigabit per second) and long distance(up to 10 km) Standard provides definitions about physical layer characteristics, transport control protocol, and upper level interface to TCP/IP, SCSI, and other protocolsSome features are not specified(routing algorithm, internal switch architecture)

Fibre Channel (cont.)

Switching Mechanismvirtual cut-through: incoming messages are forwarded as soon as they are routed and out port is free

Flow Control Mechanismcredit scheme

System Model

Switch Architecture

Network Topology

Routing Algorithm

Communication Pattern

Disk response time model

I/O load generation

Switch Architecture

Switch Architecture

Network Topology

Single roomRegular:

Fattrees, meshes, multistage networks, and fully connected topologies

Irregular: randomly generated, a single link connects two

switches

Floor topologies

Routing Algorithm

Distributed routingLeaving routing decisions to each switch

Up*/down* routing (partially adaptive)Based on breadth-first spanning tree(BFS)

Minimal adaptive routing (fully adaptive)

Communication Pattern

Request parameters:Disk IDAccess type (read or write)Starting location (sector number)Requested size

Communication Pattern

Disk Response Time Model

A single server queue with a FIFO discipline service

Composed of three parts: Seek timeRotational latencyTransfer time

Disk Response Time Model

I/O Load Generation

Use auto-similar arrival patternReal traffic is bursty and the bursts exist over many

time scales

Model each server as a set of ON/OFF sourcesModel the length of ON/OFF periods with Pareto distributionSimulator can be feed with real-world I/O traces

Evaluating SANs Performance

Effect of switch architectures on performance

Effect of faulty links on performance

Effect of Switch architecture

Effect of Switch architecture

Effect of Failures in Links

Effect of Failures in Links

Summary

SAN is a alternative to traditional server-to-disk approach

Fibre channel is a prominent technology for implementing SAN.

The simulator considers a wide set of characteristics and is a key tool for the design and evaluation of SANs.

Questions

What is a storage area network?

What are the limitations of traditional server-storage architecture?

Name some features of fiber channels.