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. © 2003, Cisco Systems, Inc. All rights reserved. 1

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

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

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.

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?

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?

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 …

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)

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 …

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?

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

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

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.