Storage Area Networks

Chapter 1 - Introduction

ContentsServer-centric IT architecture and Its Limitations

Storage-centric IT architecture and Its Advantages

Case study: Replacing a server with Storage Networks

The Data Storage and the Data Access Problem

The Battle for size and access.

Importance of DataStored data and information that it contains are the prized possessions for a company.

The computers necessary for data processing can be purchased at any time.

If stored data is lost, getting it back is infinitely more expensive and time consuming.

Data networks must be designed with built-in redundancy and for high availability.

What is storage?In a computer, storage is the place where data is held in an electromagnetic or optical form for access by the processor.

Storage is divided into two categories: 1) Primary Fast e.g. RAM, ROM, L1 and L2 caches 2) Secondary Slow e.g. Hard disks, Diskettes, ZIP drives, RAID systems and holographic storage.

Hierarchy of Storage

What is storage? - ChallengesWhat data to keep?

How to keep the data?

Where to keep the data?

What is network?Computer network is a collection of computers and devices

- interconnected by communication channels that facilitate communications and

- allows for sharing of resources and information among interconnected devices.

Types of networks: LAN, MAN, WAN

Client Server Model

Directly connected storage in traditional client server environments.

Connectivity and Communication in Client Server ModelThe server uses the I/O bus to connect with a storage device.

The server communicates with the storage through a device-specific language or protocol.

What is storage network?Paradigm shift in how data is stored and accessed within computer systems.

Storage devices are connected directly to an existing network or through its own storage network.

Storage networking Technologies

Two distinct models

Network-Attached Storage NAS

Storage Area Networks SAN.

1) Network-Attached Storage NAS

It allows storage to be placed onto an existing client/server network.

Based upon Ethernet standards utilizing standard TCP/IP network protocols.

1) Network-Attached Storage NAS

NAS example showing enhancements to data access

2) Storage Area Network - SAN

SANs create a unique network just for storage.

SANs are based on a protocol called Fibre Channel.

Storage Area Network - SAN It is a specialized high-speed network connecting servers and storage devices.

It is the network behind the servers.

Its primary purpose is the transfer of data between computer systems and storage elements.

It consists of - a communication infrastructure , which provides connections, and - a management layer, which organizes the connections, storage elements, and computer systems.

NAS vs SAN

Sl NoNASSAN1An Independent deviceA network of storage devices2Attached on the primary LANActs as a secondary network to LAN3Connected by EthernetConnected by Fibre Channel or iSCSI4NAS appears as a single node on networkSAN appears as an extra storage for each server.5Best suited for file sharing and applications involving data transfer of short duration and volumeBest suited for data intensive applications and mission critical database applications

1) Server Centric IT architectureClient Server Model

1) Server Centric IT architectureStorage devices are connected to servers by means of SCSI cables.

1) Server Centric IT architectureStorage device exists only in relation to the server to which it is connected.

Other servers cannot directly access the data; they always have to go through the server that is connected to the storage device.

1) Server-Centric Its limitationsThe server (s) connected to the storage devices may fail, leading to the loss of valuable data.

Storage capacity that can be connected to a computer is limited because --- Each computer can accommodate only a limited number of I/O cards. ---The length of SCSI cables is limited to a maximum of 25m.

A computer cannot access storage devices that are connected to a different computer.

1) Server-Centric Its limitations

The storage capacity on server 2 is full. It cannot make use of the fact that there is still storage space free on server 1 and server 3

2) Storage Centric IT architectureStorage devices exist completely independent of any computer

The SCSI cable is replaced by a network that is installed in addition to the existing LAN.

The network is primarily used for data exchange between computers and storage devices.

IT architectures with storage networks.

2) Storage Centric IT architecture

2) Storage Centric IT architectureMany small hard disks attached to the computers are replaced by a large disk subsystem.

The storage network permits all computers to access disk subsystem and share it.

Replacing a server with storage networks

(1)The old server is connected to a storage device via a storage network

(2) The new server is assembled and connected to the storage network (3) To generate test data the production data is copied within the storage device.

Replacing a server with storage networks

(4) Old server and new server share the storage system. The new server is intensively tested using the copied production data

Replacing a server with storage networks

Finally, (5) The old server is powered down and (6) The new server is started up with the production data.