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1、Direct Attached Storage and Introduction to SCSI,Module 2.1,DAS and Introduction to SCSI,- 2,DAS and Introduction to SCSI,Upon completion of this module, you will be able to: Discuss the benefits and challenges of DAS Discuss DAS management options Discuss evolution of SCSI Describe SCSI 3 architect
2、ure Discuss SCSI addressing and communication model,DAS and Introduction to SCSI,- 3,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,DAS and Intr
3、oduction to SCSI,- 4,What is DAS?,Uses block level protocol for data access,Internal Direct Connect,DAS and Introduction to SCSI,- 5,DAS Benefits,Ideal for local data provisioning Quick deployment for small environments Simple to deploy Reliability Low capital expense Low complexity,DAS and Introduc
4、tion to SCSI,- 6,DAS Connectivity Options,ATA (IDE) and SATA Primarily for internal bus 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 and Introduction to SCSI,- 7,DAS Ma
5、nagement,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 and Introduction to SCSI,- 8,DAS Challenges,
6、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,DAS a
7、nd Introduction to SCSI,- 9,Lesson Summary,Key points covered in this lesson: Internal and External DAS DAS Benefit DAS Management Options DAS Limitations,DAS and Introduction to SCSI,- 10,Lesson: Introduction to SCSI,Upon completion of this module, you will be able to: Describe SCSI-3 architecture
8、Discuss SCSI device models with different port configurations Describe SCSI Addressing,DAS and Introduction to SCSI,- 11,Evolution of Parallel SCSI,Developed by Shugart Associates & named as SASI ANSI acknowledged SCSI as an industry standard SCSI versions SCSI1 Defined cable length, signaling chara
9、cteristics, commands, & transfer modes Used 8-bit narrow bus with maximum data transfer rate of 5 MB/s SCSI2 Defined Common command Set (CCS) Improved performance, reliability, and added additional features SCSI3 Latest version of SCSI Comprised different but related standards, rather than one large
10、 document.,DAS and Introduction to SCSI,- 12,SCSI Interfaces (Parallel),DAS and Introduction to SCSI,- 13,SCSI Chain,DAS and Introduction to SCSI,- 14,SCSI Connectors,DAS and Introduction to SCSI,- 15,SCSI Connectors (cont.),DAS and Introduction to SCSI,- 16,SCSI Connectors (cont.),DAS and Introduct
11、ion to SCSI,- 17,SCSI-Bus Interface Connector,SCA (Single Connector Attached),W (Wide),N (Narrow),DAS and Introduction to SCSI,- 18,SCSI Signaling,Single Ended Single-ended SCSI allows devices to be attached to a total cable length up to six meters or only three meters, depending on type. Single-end
12、ed signaling uses data and ground lines. High Voltage Differential Signaling (HVDS) Also called just “differential SCSI“ because it was available before there was a second differential option, HVDS supports cable lengths up to 25 meters. In order to increase distance, differential signaling uses dat
13、a low and data high lines and costs more than single-ended. Low Voltage Differential Signaling (LVDS) Ultra2 SCSI introduced LVDS, which supports cable lengths up to only 12 meters. LVDS requires less power and is less costly than HVDS, because the transceivers are built into the controller chips.,D
14、AS and Introduction to SCSI,- 19,SCSI Signaling,DAS and Introduction to SCSI,- 20,SCSI3 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 suc
15、h as electrical signaling methods and data transfer modes,DAS and Introduction to SCSI,- 21,SCSI target device Executes commands issued by initiators Examples: SCSI peripheral devices Device requests contain Command Descriptor Block (CDB),SCSI Device Model,SCSI communication involves: SCSI initiator
16、 device Issues commands to SCSI target devices Example: SCSI host adaptor,DAS and Introduction to SCSI,- 22,SCSI Device Model (Cont.),CDB structure 8 bit structure Contain operation code, command specific parameter and control parameter SCSI Ports SCSI device may contain initiator port, target port,
17、 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,
