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 network Optimized 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 server Bandwidth saturation during backups

Typical SAN Architecture

Fibre Channel Generic transport mechanism Provides 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 protocols Some features are not specified(routing algorithm, internal switch architecture)

Fibre Channel (cont.) Switching Mechanism virtual cut-through: incoming messages are forwarded as soon as they are routed and out port is free Flow Control Mechanism credit 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 room Floor topologies Regular: Irregular: Fattrees, meshes, multistage networks, and fully connected topologies Irregular: randomly generated, a single link connects two switches Floor topologies

Routing Algorithm Distributed routing Leaving 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 ID Access 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 time Rotational latency Transfer time

Disk Response Time Model

I/O Load Generation Use auto-similar arrival pattern Real traffic is bursty and the bursts exist over many time scales Model each server as a set of ON/OFF sources Model the length of ON/OFF periods with Pareto distribution Simulator 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.