© 2009 EMC Corporation. All rights reserved. Direct Attached Storage and Introduction to SCSI Module 2.1

© 2009 EMC Corporation. All rights reserved. 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 architecture  Discuss SCSI addressing and communication model

© 2009 EMC Corporation. All rights reserved. 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 4 What is DAS?  Uses block level protocol for data access Internal Direct Connect External Direct Connect

© 2009 EMC Corporation. All rights reserved. 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 7 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 8 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 9 Lesson Summary Key points covered in this lesson:  Internal and External DAS  DAS Benefit  DAS Management Options  DAS Limitations

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 10 Lesson: Introduction to SCSI Upon completion of this module, you will be able to:  Describe SCSI-3 architecture  Discuss SCSI device models with different port configurations  Describe SCSI Addressing

© 2009 EMC Corporation. All rights reserved. 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 – 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.

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 12 SCSI Interfaces (Parallel) InterfaceStandardWidthClock MAX Throughput MAX Devices SCSI-1SCSI-1 (1986)8 5 MHz 5 MB/s 8 Fast SCSISCSI-2 (1994)8 10 MHz 10 MB/s 8 Fast-Wide SCSI SCSI-2; SCSI-3 SPI (1996) MHz 20 MB/s 16 Ultra SCSISCSI-3 SPI8 20 MHz 20 MB/s 8 Ultra Wide SCSI SCSI-3 SPI16 20 MHz 40 MB/s 16 Ultra2 SCSI SCSI-3 SPI-2 (1997) 8 40 MHz 40 MB/s 8 Ultra2 Wide SCSI SCSI-3 SPI MHz 80 MB/s 16 Ultra3 SCSI SCSI-3 SPI-3 (1999) MHz DDR 160 MB/s 16 Ultra-320 SCSI SCSI-3(2002)16 80 MHz DDR 320 MB/s 16 Ultra-640 SCSI SCSI-3(2003) MHz DDR 640 MB/s 16

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 13 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 14  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 device – Issues commands to SCSI target devices – Example: SCSI host adaptor

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 15 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, 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 16 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 IDTarget ID LUN Target Initiator LUNs

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 17 SCSI Addressing Example Initiator IDTarget ID LUN c0c0 t0t0 d0d0 Port Host Storage 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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 18 SCSI Command Model  The SCSI command model is defined with the CDB Operation Code 1 Command Specific-Parameters n–1 n Control Bit Byte

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 19 Operation Code  The operation code consists of a group and command code fields. Bit Group Code Command Code Group Code Command-Specific Parameters 0 6 bytes 1 and 2 10 bytes 3 Reserved 4 16 bytes 5 12 bytes 6 and 7 Vendor specific

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 20 Common SCSI Commands Command Description READ Reads data from a device WRITE Writes data to a device TEST UNIT READY Queries the device to check whether it is ready for data transfer INQUIRY Returns basic information, which is also used to ping the device REPORT LUNS List the logical unit numbers SEND AND RECEIVE DIAGNOSTIC RESULTS Runs a simple self-test or a specialized test defined in a diagnostic page FORMAT UNIT Sets all sectors to all zeroes and allocates logical blocks, avoiding defective sectors LOG SENSE Returns current information from log pages LOG SELECT Used to modify data in the log pages of a SCSI target device MODE SENSE Returns current device parameters from mode pages MODE SELECT Sets device parameters on a mode page

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 21 Control Field & Status Bit Vendor Specific Reserved NACA Obsolete Link Status Byte CodesStatus 0h GOOD 2h CHECK CONDITION 4h CONDITION MET 8h BUSY 10h INTERMEDIATE 14h INTERMEDIATE-CONDITION MET 18h RESERVATION CONFLICT 22h COMMAND TERMINATED 28h TASK SET FULL 30h ACA ACTIVE All other codes Reserved

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 22 Lesson Summary Key points covered in this lesson:  SCSI – 3 Architecture  SCSI device model  SCSI addressing  SCSI command model

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 23 Module Summary Key points covered in this module:  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

© 2009 EMC Corporation. All rights reserved. DAS and Introduction to SCSI - 24 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?