1. Direct Attached Storage Overview
Introduction
This lesson provides the learner with an overview of Direct Attached Storage (DAS). This lesson includes a definition of DAS, DAS architecture, protocols, and the advantages and disadvantages of DAS.
Importance
Understanding the concepts of DAS and the limitations of DAS technology will help a Systems Engineer (SE) understand why NAS and SAN solutions have evolved, as well increasing SE credibility by showing an awareness of systems other than SAN.
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2. Lesson Objectives
Upon completion of this lesson, you will explain DAS solutions by explaining DAS, its characteristics, and listing its advantages and disadvantages.
Performance Objective
Upon completion of this lesson, you will explain DAS solutions by explaining DAS, its characteristics, and listing its advantages and disadvantages.
Enabling Objectives
Give a brief explanation of DAS solutions
Explain the fundamental characteristics of DAS architectures
Explain the basic storage protocols ATA, SCSI, FC, ESCON/FICON
Explain the advantages of DAS architectures
Explain the disadvantages of DAS architectures

3. Lesson Outline What is DAS? DAS architecture Storage protocols
DAS advantages
DAS disadvantages
Summary
Prerequisites
The qualifications to attend the program.

4. What is DAS? DAS solutions provide: DAS = Direct Attached Storage
Low-cost, slow to medium speed storage for use in home computers and small businesses
Can provide higher-cost, high-performance storage, which can be used in solutions needing high-speed access
What is DAS?
Objective
Give a brief explanation of DAS solutions.
Introduction
This section provides a high level explanation of DAS.
Facts
DAS is storage attached directly to the computer, hence the name "Direct Attached Storage" (DAS). The only server that has access to a DAS device is the server to which it is attached. It is captive to that server.
DAS solutions provide low-cost, slow to medium speed storage for use in home computers and small business. It can also provide higher-cost, high-performance storage, which can be used in solutions needing high-speed access.

5. Direct Attached Storage
What is DAS? (cont.) FC
Clients
SCSI
Direct Attached Storage
Servers
IP Network
Win2k
Linux
Unix
ATA/IDE
less expensive
more expensive
Main Frame
The "typical" storage environment
What is DAS? (cont.)
Facts
DAS is very common in storage environments. In these environments, DAS is captive 'behind' the server.
The server CPU must handle user I/O requests, and also:
User database inquiries
User file/print serving
Data integrity checking
Communication with other devices
Data access is file system and platform dependant, which is costly to scale and complex to manage.
Practice Items
What does DAS stand for?
To how many servers is a DAS device available?
With which protocols are DAS devices compatible?

6. DAS Architecture
DAS uses an I/O Channel architecture, which resides between a computer (initiator) and the device (target) used to store its data.
Storage device is only accessible by attached host computer.
I/O Channel
DAS Architecture
Objective
Explain the fundamental characteristics of DAS architectures.
Introduction
This section discusses the basic characteristics of DAS and typical DAS architectures.
Facts
DAS is the most basic storage solution. As the name implies, storage devices are directly attached to the computer system. The basic components of DAS are the storage device and the Input/Output (I/O) interface that connects the storage device to the computer system.
DAS uses an I/O Channel to connect the host to the storage device. The DAS connections are either internal to the computer casing or external. The storage device can only be accessed by the attached host computer, hence the name "captive storage“. In DAS, storage is connected to each server and the file system on each server only communicates with the storage directly attached to it. DAS does notdirectly share storage resources or data.
DAS comes in many forms including: SCSI, ATA/IDE, FC, ESCON/FICON, and serial storage architecture (SSA). Modern DAS are typically ATA/IDE or SCSI, but they can be FC.
Practice Items
Where are the DAS I/O connections located?

7. Storage Protocols
Most DAS products are built with one of the following common storage protocols:
ATA (IDE)
SCSI
fibre Channel
ESCON/FICON
Storage Protocols
Objective
Explain the basic storage protocols ATA, SCSI, FC, ESCON/FICON
Introduction
This section provides basic explanations of the most common storage protocols in DAS environments
Facts
The majority of disk storage products offered by drive manufactures are built using one several common protocols, including ATA (IDE), SCSI, FC, ESCON and FICON.
Advanced Technology Attachment (ATA) is the official name that the American National Standards Institute (ANSI) uses for what the computer industry calls Integrated Drive Electronics (IDE). ATA and IDE are different acronyms that describe the same attachment interface. ATA (IDE) drives have a relatively slower data transfer rates than SCSI, and are targeted for the high-volume, low cost market. ATA (IDE) drives are found in most home and office personal computers.
The Small Computer System Interface (SCSI—pronounced SKUH-zee and sometimes colloquially known as "scuzzy"), is a set of ANSI standard electronic interfaces that allow personal computers to communicate with peripheral hardware such as disk drives, tape drives, CD-ROM drives, printers, and scanners. SCSI drives are more expensive and offer high data transfer rate. These drives are more expensive and are targeted towards high-end systems.
fibre Channel (FC) is an ANSI standard for serial gigabit transport of data between computer devices. FC is especially well suited for connecting servers to shared storage devices.
Continued …

8. DAS Advantages Simple implementation Familiarity Mature technology
Deterministic performance
DAS advantages
Objective
Explain the advantages of DAS architectures.
Introduction
This section provides a brief description of the advantages of DAS implementations.
Facts
The advantages of DAS include:
Simple implementation
IT personnel are familiar with DAS
It is a mature technology, and thus has a large installed base
Has what can be called deterministic performance (fixed access latencies, guaranteed bandwidth)

9. DAS Disadvantages Distance Flexibility Manageability Backups ROI
System downtime
DAS Disadvantages
Objective
Explain the disadvantages of DAS architectures.
Introduction
This section covers the major disadvantages of DAS
Facts
The major disadvantages of DAS include:
Distance is only short to medium
Flexibility
Device count—the number of devices that can be attached is limited.
Capacity utilization (captive capacity). Captive storage is a major disadvantage to DAS. The DAS storage is only available to the computer that it is attached to. If other users need additional storage (or capacity) they cannot access the DAS located on different computers.
DAS is difficult to upgrade.
Manageability. Discrete management requirement. As a DAS system grows it becomes increasingly unwieldy in that the system becomes difficult to manage, and maintain. It become less reliable, and ultimately is unable to keep up with organizational requirements.
Continued …

10. What is DAS? (Practice) Answer the following questions:
What does DAS stand for?
To how many servers is a DAS device available?
With which protocols are DAS devices compatible?
Practice - What is DAS?

11. Storage Protocols Practice
Match the protocols on the left with the correct item on the right
ATA
Fibre Connectivity is a high speed I/O interface for mainframe computer connections to storage device
SCSI
targeted for the high-volume, low cost market
Fibre Channel
a set of ANSI standard electronic interfaces that allow personal computers to communicate with peripheral hardware
ESCON
a set of IBM and vendor products that interconnect S/390 computers with each other and attached storage
FICON
an ANSI standard for serial gigabit transport of data between computer devices
Practice - Storage Protocols Practice

12. Lesson Practice In groups of two, discuss the following: What is DAS?
What protocols are used with DAS?
What are the advantages and disadvantages of DAS?
Be prepared to summarize and share your answers for the class
DAS Lesson Practice

13. Summary This lesson presented these key points:
DAS = Direct Attached Storage
DAS connections are external or internal
Storage protocols are ATA, SCSI, FC and ESCON/FICON
While DAS has advantages, there are a decided number of limitations to DAS
Summary: DAS Overview
Review
In this lesson, you learned how to explain the basics of DAS storage systems. This lesson covered a definition of DAS, DAS architecture, protocols, and the advantages and disadvantages of DAS.