Department of ISE B.E. 7h Semester

INTERNAL ASSESSMENT TEST – 2

Date: 3rd

Oct, 2017 Max Marks: 50

Subject & Code: Storage Area Networks / 10IS765 Section: 7th

A & B

Name of faculty: Prof. Animesh Giri Time: 8:30 AM – 10:00 AM

Note: ANSWER ANY FIVE FULL QUESTIONS

SOLUTIONS

1. Explain the SCSI-3 standards architecture along with its SCSI-3 Client-Server Model.

(10 Marks) Answer:

SCSI – 3 Architecture

o SCSI command protocol

o Primary commands common to all devices

o Transport layer protocol

o Standard rules for device communication and information sharing

o Physical layer interconnect

o Interface details such as electrical signaling methods and data transfer modes

SCSI Device Model

USN 1 P E

PESIT- Bangalore South Campus Hosur road, 1km before Electronic City, Bengaluru -100

Department of Information Science & Engineering

Department of ISE B.E. 7h Semester

o Device requests uses Command Descriptor Block (CDB)

o 8 bit structure

o Contain operation code, command specific parameter and control parameter

o SCSI Ports

o SCSI device may contain initiator port, target port, target/initiator port

o Based on the port combination, a SCSI device can be classified as an initiator model, a

target model, a target model with multiple ports or a combined model (target/initiator

model). Example:

o Target/initiator device contain target/initiator port and can switch orientations

depending on the role it plays while participating in an I/O operation

o To cater to service requests from multiple devices, a SCSI device may also have multiple

ports (e.g. target model with multiple ports)

2. Explain the components of Storage Area Networks (SAN)? Illustrate transmission of

data in Fibre Channel Arbitrated Loop (FC-AL) configuration with a neat diagram.

(10 Marks)

Department of ISE B.E. 7h Semester

Answer:

o Dedicated high speed network of servers and shared storage devices

o Provide block level data access

o Resource Consolidation

o Centralized storage and management

o Scalability

o Theoretical limit: Appx. 15 million devices

o Secure Access

Components of SAN: Node ports

Department of ISE B.E. 7h Semester

Department of ISE B.E. 7h Semester

FC- AL Transmission

o Fibre Channel Arbitrated Loop (FC-AL)

o Devices must arbitrate to gain control

o Devices are connected via hubs

o Supports up to 127 devices

Department of ISE B.E. 7h Semester

3. Discuss the layers of Fibre Channel Protocol Stack; also explain different types of Fibre

Channel Ports with a neat diagram. (10 Marks)

Answer:

o FC uses channel technology

o Provide high performance with low protocol overheads

o FCP is SCSI-3 over FC network

o Sustained transmission bandwidth over long distances

o Provides speeds up to 8 Gb/s (8 GFC)

o FCP has five layers:

o FC-4 – Upper Layer

o FC-2 - Transport Layer

o FC-1 – Transmission Protocol

o FC-0 – Physical Interface

Department of ISE B.E. 7h Semester

*FC-3 is not yet implemented

Fibre Channel Ports

4. What is Network-attached storage (NAS)? What are the benefits of NAS? Explain the

factors affecting NAS performance and availability with a neat diagram.

(10 Marks)

Answer:

Department of ISE B.E. 7h Semester

Benefits of NAS

o Support comprehensive access to information

o Improves efficiency – uses special purpose OS

o Improved flexibility – platform independent

o Centralizes storage

o Simplifies management

o Scalability

o High availability – provide redundant components

Provides security integration to environment (user authentication and authorization)

Factors affecting NAS performance & Availability

1. Number of Hops

2. Authentication with Directory services like LDAP, Active Directory or NIS

3. Retransmission

4. Over-utilized Routers & Switches

5. File Directory Lookup & Metadata request

6. Over-Utilized NAS devices

7. Over-Utilized Clients

Department of ISE B.E. 7h Semester

5. Explain Network-attached storage (NAS) file sharing protocols; also illustrate how NAS

device manage these protocols for handling the file I/O requests to a remote file system.

(10 Marks)

Answer:

Department of ISE B.E. 7h Semester

NAS File Sharing Protocols

o Two common NAS file sharing protocols are:

o NFS – Network File System protocol

o Traditional UNIX environment file sharing protocol

o CIFS – Common Internet File System protocol

o Traditional Microsoft environment file sharing protocol, based upon the Server

Message Block protocol

NFS

• NFS is a client/server protocol for file sharing that is most commonly used on UNIX

systems.

• NFS was originally based on the connectionless User Datagram Protocol (UDP).

• It uses a machine-independent model to represent user data.

• It also uses Remote Procedure Call (RPC) as a method of interposes communication

between two computers.

• The NFS protocol provides a set of RPCs to access a remote file system for the

following operations:

1. Searching files and directories

2. Opening, reading, writing to, and closing a file

3. Changing file attributes

4. Modifying file links and directories

• NFS uses the mount protocol to create a connection between the client and the remote

system to transfer data.

• NFS (NFSv3 and earlier) is a stateless protocol, which means that it does not maintain

any kind of table to store information about open files and associated pointers.

• Therefore, each call provides a full set of arguments to access files on the server.

• These arguments include a file name and a location, a particular position to read or write,

and the versions of NFS.

• Currently, three versions of NFS are in use:

Department of ISE B.E. 7h Semester

1. NFS version 2 (NFSv2): Uses UDP to provide a stateless network connection

between a client and a server. Features such as locking are handled outside the

protocol.

2. NFS version 3 (NFSv3): The most commonly used version, it uses UDP or

TCP, and is based on the stateless protocol design. It includes some new

features, such as a 64-bit file size, asynchronous writes, and additional file

attributes to reduce re-fetching.

3. NFS version 4 (NFSv4): This version uses TCP and is based on a stateful

protocol design. It offers enhanced security.

CIFS

• CIFS is a client/server application protocol that enables client programs to make requests

for files and services on remote computers over TCP/IP.

• It is a public, or open, variation of Server Message Block (SMB) protocol.

• The CIFS protocol enables remote clients to gain access to files that are on a server.

• CIFS enables file sharing with other clients by using special locks

• File names in CIFS are encoded using unicode characters.

• CIFS provides the following features to ensure data integrity:

1. It uses file and record locking to prevent users from overwriting the work of

another user on a file or a record.

2. It runs over TCP.

3. It supports fault tolerance and can automatically restore connections and reopen

files that were open prior to interruption. The fault tolerance features of CIFS

depend on whether an application is written to take advantage of these features.

Users refer to remote file systems with an easy-to-use file naming scheme:

\\server\share or \\servername.domain.suffix\share.

Department of ISE B.E. 7h Semester

6. Explain iSCSI Protocol Stack; also illustrate how iSCSI devices are discovered by using

iSNS Server in an IP Network. (10 Marks)

Answer:

iSCSI is an IP-based protocol that establishes and manages connections between storage, hosts, and

bridging devices over IP.

iSCSI carries block-level data over IP-based networks, including Ethernet networks and the

Internet.

iSCSI is built on the SCSI protocol by encapsulating SCSI commands and data in order to allow

these encapsulated commands and data blocks to be transported using TCP/IP packets.

Department of ISE B.E. 7h Semester

• Host (initiators), targets, and an IP-based network are the principal iSCSI components.

• The simplest iSCSI implementation does not require any FC components.

• If an iSCSI-capable storage array is deployed, a host itself canact as an iSCSI initiator,

and directly communicate with the storage over an IP network. However, in complex

implementations that use an existing FC array for iSCSI connectivity, iSCSI gateways or

routers are used to connect the existing FC SAN.

• These devices perform protocol translation from IP packets to FC packets and vice-versa,

thereby bridging connectivity between the IP and FC environments.

Internet Storage Name Server

� For iSCSI communication, initiator must discover location of the target on a network

� iSCSI discovery take place in two ways:

– SendTargets discovery

� initiator is manually configured with the target

– Internet Storage Name Service (iSNS)

� Initiators and targets automatically register themselves with iSNS server

� iSNS is a client/server model

� An iSNS server can be hosted on a target, initiator, or stand-alone server with a specified IP

Department of ISE B.E. 7h Semester

address

7. Define Content-Addressed Storage (CAS). Illustrate with an example the process of storing

the data objects on CAS and the data object retrieval from the CAS system. (10 Marks)

Answer:

What is Content Addressed Storage (CAS)

o Object-oriented, location-independent approach to data storage

o Repository for the “Objects”

o Access mechanism to interface with repository

o Globally unique identifiers provide access to objects

Benefits of CAS

o Content authenticity

o Content integrity

o Location independence

o Single-instance storage (SiS)

o Retention enforcement

o Record-level protection and disposition

o Technology independence

Department of ISE B.E. 7h Semester

o Fast record retrieval

Department of ISE B.E. 7h Semester

8. Define storage virtualization. Explain Block- Level Storage Virtualization & File- Level

Storage Virtualization with a neat diagram. (10 Marks)

Answer:

Department of ISE B.E. 7h Semester

Department of ISE B.E. 7h Semester