Storage Networking Technologies and Virtualization Section 2 DAS and Introduction to SCSI1.

DAS and Introduction to SCSI 1

Storage Networking Technologies and Virtualization

Section 2

DAS and Introduction to SCSI - 2

Section Objective

Upon completion of this section, you will be able to:• Describe the elements, connectivity, and

management of:– Direct Attached Storage (DAS)– Network Attached Storage (NAS)– FC and IP Storage Area Networks (SAN)– Content Addressed Storage (CAS) and

• Discuss the benefits and challenges of each of the storage models

• Describe various virtualization technologies


Direct Attached Storage and Introduction to SCSI

Chapter 5


Chapter Objective

Upon completion of this chapter, you will be able to:

• Discuss the benefits and challenges of DAS• Discuss DAS management options• Discuss evolution of SCSI• Describe SCSI – 3 architecture• Discuss SCSI addressing and communication

model


Lesson: Direct Attached Storage

Upon completion of this lesson, you will be able to:

• Discuss the benefits of DAS• Describe the elements of DAS• Discuss DAS management considerations• Discuss DAS challenges


What is DAS?6

• Uses block level protocol for data access

Internal Direct Connect External Direct Connect


DAS Benefits

• Ideal for local data provisioning• Quick deployment for small environments• Simple to deploy • Reliability• Low capital expense• Low complexity


DAS Connectivity Options

• ATA(133 MB/sec) (IDE) and SATA(150 MB/sec too 600)– Primarily for internal bus (40pin-disk to MB,34pin-drive to MB)(latest ATA Ultra DMA/133)

• SCSI– Parallel (primarily for internal bus)– Serial (external bus)

• FC– High speed network technology

• Buss and Tag – Primarily for external mainframe– Precursor to ESCON and FICON


DAS Management• Internal – Host provides:• Disk partitioning (Volume management)• File system layout

– Direct Attached Storage managed individually through the server and the OS

• External– Array based management– Lower TCO for managing data and storage

Infrastructure


DAS Challenges

• Scalability is limited– Number of connectivity ports to hosts– Number of addressable disks– Distance limitations

• Downtime required for maintenance with internal DAS

• Limited ability to share resources– Array front-end port, storage space– Resulting in islands of over and under utilized storage

pools


Lesson Summary

Key points covered in this lesson:• Internal and External DAS • DAS Benefit• DAS Management Options• DAS Limitations


Lesson: Introduction to SCSI

Upon completion of this lesson, you will be able to:

• Describe SCSI-3 architecture• Discuss SCSI device models with different port

configurations• Describe SCSI Addressing


Evolution of Parallel SCSI• Developed by Shugart Associates & named as SASI• ANSI acknowledged SCSI as an industry standard• SCSI versions

– SCSI–1• Defined cable length, signaling characteristics, commands, & transfer

modes• Used 8-bit narrow bus with maximum data transfer rate of 5 MB/s

– SCSI–2• Defined Common command Set (CCS)• Improved performance, reliability, and added additional features

– SCSI–3• Latest version of SCSI,• Comprised different but related standards, rather than one large

document.


SCSI–3 Architecture

• SCSI command protocol– Primary commands common to all devices

• Transport layer protocol– Standard rules for device communication and information sharing

• Physical layer interconnect– Interface details such as electrical signaling methods and data transfer modes

SCSI Primary Commands

SCSI Specific Commands

Physical Layer

SCSI-3 Command Protocol

Transport LayerCommon Access Method

SCSI Architectural Model

SCSI-3 Protocol

Fibre ChannelProtocol

Serial BusProtocol

GenericPacketized

Protocol

SCSI-3 Parallel

Interface

IEEE Serial Bus

Fibre Channel


SCSIInitiator Device

SCSITarget Device

ApplicationClient

Logical UnitDevice Service

Response

Device Service Request

Task Management Request

Task Management Response

DeviceServer

TaskManager

• SCSI target device– Executes commands issued by initiators– Examples: SCSI peripheral devices

• Device requests contain Command Descriptor Block (CDB)

SCSI Device ModelSCSI communication involves: • SCSI initiator device

– Issues commands to SCSI target devices

– Example: SCSI host adaptor


SCSI Device Model (Cont.)• CDB (command descriptor Block) structure– 8 bit structure– Contain operation code, command specific parameter and control

parameter• SCSI Ports– SCSI device may contain initiator port, target port, target/initiator

port– Based on port combination device is classified– For example

• Target/initiator device contain target/initiator port and can switch orientations depending on the role it plays while participating in an I/O operation

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


SCSI Addressing

• Initiator ID - a number from 0 to 15 with the most common value being 7.• Target ID - a number from 0 to 15• LUN - a number that specifies a device addressable through a target.

Initiator ID Target ID LUN

Target Initiator LUNs


SCSI Addressing Example

Initiator ID Target ID LUN

c0 t0 d0

Port

Port

Port

Port

Port

HostStorage Array

Target (Front-end port)Target – t0

Initiator (HBA)Controller – c0

d0

d1

d2

Storage Volumes

Host Addressing:Storage Volume 1 - c0t0d0 Storage Volume 2 - c0t0d1 Storage Volume 3 - c0t0d2

LUN

LUN

LUN


Cost Overall, IDE is a much cheaper solution.

When compared with IDE, SCSI is often more expensive to implement and support.

Expansion IDE/EIDE allows 2 two devices per channel. Most computers have 2 channels.

SCSI is capable of supporting up to 7 or 15 devices.

Ease IDE is commonly a much easier product to setup than SCSI.

Configuring SCSI can be more difficult for most users when compared to IDE.

ATA/IDE SCSI


Resources All motherboards today have an ATA/IDE interface and unless additional drives are needed no additional resources need to be taken.

Unlike IDE, SCSI requires an interface expansion card in most cases (unless the motherboard already has it). This means additional system resources will be required.

ATA/IDE SCSI


Lesson Summary

Key points covered in this lesson:• SCSI – 3 Architecture • SCSI device model • SCSI addressing• Comparison of SCSI & IDE/ATA


Chapter Summary

Key points covered in this chapter:• DAS can be internal or external• Multiple hosts cannot share same storage ports• DAS is made up of a CPU, connectivity, and storage

devices • DAS connectivity uses block-level access protocols• SCSI – 3 architecture• Parallel SCSI addressing• SCSI Command model


Check Your Knowledge

• What are the physical elements of DAS?• Give an example of when DAS is a good solution.• Describe internal DAS connectivity.• Describe external DAS connectivity.• List SCSI Device Models with Different Port

Configurations.• How many devices SCSI can support?• Which SCSI ID has highest priority?

Storage Networking Technologies and Virtualization Section 2 DAS and Introduction to SCSI1.

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