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- Herausgeber: Packt Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Oracle RAC or Real Application Clusters is a grid computing solution that allows multiple nodes (servers) in a clustered system to mount and open a single database that resides on shared disk storage. Should a single system (node) fail, the database service will still be available on the remaining nodes. Oracle RAC is an integral part of the Oracle database setup. You have one database with multiple users accessing it, in real time. This book will enable DBAs to get their finger on the pulse of the Oracle 11g RAC environment quickly and easily.This book will cover all areas of the Oracle RAC environment and is indispensable if you are an Oracle DBA who is charged with configuring and implementing Oracle11g R1, with bonus R2 information included. This book presents a complete method for the configuration, installation, and design of Oracle 11g RAC, ultimately enabling rapid administration of Oracle 11g RAC environments.This practical handbook documents how to administer a complex Oracle 11g RAC environment. Packed with real world examples, expert tips and troubleshooting advice, the book begins by introducing the concept of Oracle RAC and High Availability. It then dives deep into the world of RAC configuration, installation and design, enabling you to support complex RAC environments for real world deployments. Chapters cover Oracle RAC and High Availability, Oracle 11g RAC Architecture, Oracle 11g RAC Installation, Automatic Storage Management, Troubleshooting, Workload Management and much more.
By following the practical examples in this book, you will learn every concept of the RAC environment and how to successfully support complex Oracle 11g R1 and R2 RAC environments for various deployments within real world situations.
This book is the updated release of our previous Oracle 11g R1/R2 Real Application Clusters Handbook. If you already own a copy of that Handbook, there is no need to upgrade to this book.
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Veröffentlichungsjahr: 2011
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Table of Contents
Oracle 11g R1/R2 Real Application Clusters Essentials
Oracle 11g R1/R2 Real Application Clusters Essentials
Copyright © 2011 Packt Publishing
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Packt Publishing has endeavored to provide trademark information about all the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: May 2011
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Published by Packt Publishing Ltd.
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ISBN 978-1-849682-66-4
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Cover Image by Artie Ng (<[email protected]>)
Credits
Authors
Ben Prusinski
Syed Jaffer Hussain
Reviewers
Robert de Laat
Ann L. R. McKinnell
Fairlie Rego
Ronald Rood
Acquisition Editor
Kerry George
Development Editor
Meeta Rajani
Technical Editors
Conrad Sardinha
Azharuddin Sheikh
Project Coordinator
Zainab Bagasrawala
Proofreaders
Sandra Hopper
Bernadette Watkins
Chris Smith
Indexer
Rekha Nair
Graphics
Geetanjali Sawant
Nilesh Mohite
Production Coordinator
Arvindkumar Gupta
Cover Work
Arvindkumar Gupta
About the Authors
Ben Prusinski is an Oracle Certified Professional (OCP) and database architect with more than 14 years of experience with Oracle data warehouse and Oracle E-Business applications. As a corporate database consultant, Ben has provided services to dozens of Fortune 500 clients. He is an internationally recognized expert in Oracle high availability, performance tuning, database security, and ERP implementations. As a top Oracle expert, Ben received the prestigious Oracle ACE award in 2009 in recognition of his contributions to the Oracle community. As an Oracle RAC Certified Expert (OCE), Ben is also a popular speaker at major conferences such as Oracle OpenWorld, CLOUG in Latin America, IOUG, and Oracle Collaborate OAUG (Oracle Applications User Group). Ben is also a polyglot, being fluent in several languages (Spanish, French, Korean, and English) and enjoys traveling to exotic places. In his free time, he enjoys racing in autocross events, golf, martial arts, reading, and cooking.
In addition to Oracle consulting for clients, Ben regularly updates his Oracle blog at http://oracle-magician.blogspot.com with the latest database technology tips and information to share with the Oracle community. He frequently contributes to answering questions from Oracle users on the Oracle OTN forums. He can be contacted via e-mail at <[email protected]>.
I would like to extend my thanks and appreciation, first of all to my fellow co-author Mr. Syed Jaffer Hussain who was great to work with on this book. I would also like to thank everyone at Packt who made tremendous efforts for their patience and help in the editorial process. Last but not least, my heartfelt appreciation goes out to our fantastic technical review team of Oracle experts — Fairlie Rogo, Ronald Rood, and Ann L.R. Mckinnell — who provided tons of great feedback to ensure technical accuracy and quality. I also would like to dedicate this book to all fellow Oracle DBAs and consultants who work in the trenches to solve real world Oracle issues.
I also would like to thank the many Oracle professionals who have helped me as an Oracle professional over the years to make such a book like this possible, including Julian Dyke (Oracle RAC master extraordinaire), Alex Gorbachev, Doug Hahn, Tanel Poder, Arup Nanda, Robert Freeman, Tim Hall, and all of my current and past clients who allowed me to help them with their Oracle database challenges.
Syed Jaffer Hussain is the Database Support Manager at AlInma Bank (Saudi Arabia) who has over 18 years of hands-on Information Technology (IT) experience, which also includes over 10 years as a Production Oracle DBA. Apparently he is the first person in the Middle East to be awarded the prestigious Oracle ACE award. He holds several industry recognized Oracle certifications, including Oracle 10g Certified Master (OCM), OCP DBA (v8i, 9i, 10g, and 11g), and Oracle 10g RAC Certified Expert. With broad knowledge in Oracle technologies such as RAC, DataGuard, RMAN, and Performance Tuning, he has completed several successful RAC implementations, Clusterware upgrades, and has set up disaster recovery solutions for many business-critical databases. Jaffer is a noted speaker at BrainSurface.com, and occasionally presents Oracle University five-day courses and one-day celebrity seminars on behalf of Oracle EMEA. He has also worked for a couple of multinational banks in Saudi Arabia.
Jaffer frequently contributes at Oracle OTN forums and many other Oracle-related forums. He regularly updates his Oracle technology-related blog, (http://jaffardba.blogspot.com) and he is reachable at <[email protected]>.
First and foremost, I owe a very big thank you to my wife Ayesha and my three sons (Ashfaq, Arfan, and Aahil) for sacrificing their invaluable time and allowing me to concentrate on the book. I am also thankful to Alinma Bank management; in particular Ahmed Darwish and my immediate boss Mr. Majed Saleh AlShuaibi for their constant encouragement and continuous support. My special thanks goes to my younger brother Sabdar and my friend Khusro Mohammed Khan (who are also Oracle DBAs) for preparing required platforms, testing codes and doing initial review of the chapters. I also want to thank all my colleagues, Mohammed Farooqui, Zaheer, Khaja Mainuddin, Shaukat Ali, Naresh Kumar Markapuram, Hussain AlKalifah, Faisal Bakhashwain, Naser Ali AlEssa, Mohammed Alsalahi, Wayne Philips, Chand Basha, Rizwan Siddiqi, Sadak, Anees, Shakir, Angelo G Train, Mohammed Khidir, Asad Khan, Ibrahim Ali, Rajesh Ankuru, Sandeep, Mohammad AlHiary, Ahmed Khanj, Ahmed Bakheet, Mohammed Azar, and other friends for their encouragement and motivation.
I thank all the staff at Packt Publishing who were involved with this book and special mention to James Lumsden, Kerry George, Meeta Rajani, Zainab Bagasrawala, and Azharuddin Sheikh for being patient with me during the course of this book.
Last but not the least, I also thank other RAC Book authors (not in any particular order), Murali Vallath, K. Gopalakrishnan, Nitin Vengulkar, Julian Dyke, Sandesh Rao, Arup Nanda, Bert Scalzo, Riyaj Shamsudeen, Tariq Farooq, and other Oracle experts worldwide for being my inspiration.
About the Reviewers
Robert de Laat is an experienced DBA, working with Oracle products for 12 years, primarily in large, complex environments where high availability is mandatory. With a background as an Unix administrator, he is skilled in system design, high availability, and getting the most out of an environment. Robert has been working with every version of RAC, primarily on Unix/Linux platforms. He has skills in many scripting languages, such as Perl, Python, Shell, and so on. He also knows his way in PL/SQL.
Currently Robert is a senior consultant, working for Ciber in The Netherlands, where he cooperates in many complex projects for large companies where high availability is a key to the customers' success. Ciber (CBR) is an Oracle Platinum Partner and committed to the limit.
Besides spending time with Oracle, Robert enjoys woodworking and jewellery. Creating things gives him great pleasure, in his work and in his personal life. He also maintains his own website at www.dutchdba.nl, where he writes about technical stuff such as Oracle, Linux, Scripting, and so on.
I would like to thank my wife, Jose for having the patience while I spend many hours in my test lab. You truly are the light of my life.
Ann L. R. McKinnell has been an OCP since Oracle 7.3.4, with over eight years experience as a senior technical member of Oracle Global Support, specializing in Database Server technologies. Ann has trained Oracle Support and Consulting personnel from many countries in Database Internals and Problem Solving techniques. She has served as a technical reviewer for Oracle University course material, numerous My Oracle Support (previously Metalink) notes and whitepapers, and various Oracle Database Administration user manuals. Ann is also a co-author of Packt Publishing’s Oracle 11g Streams Implementer’s Guide. With over 16 years in the IT industry, Ann continues to specialize in practical implementation strategies and the development of distributed Oracle database systems, and database architecture, along with software and database design, integration, and engineering.
Fairlie Rego is a senior Oracle Database Consultant with over 10 years of experience in Oracle Database Technologies. He has worked on mission-critical, highly available systems built around the Maximum Availability architecture propounded by Oracle.
He has worked extensively in the financial, telecom, and educational sectors and has been fortunate to work in challenging environments that make use of state-of-the-art technologies.
I would like to thank my parents who have always encouraged me in my endeavors. I would also like to acknowledge my wife, Abigail for demonstrating extreme patience, given my very hectic work schedule.
Ronald Rood is an innovative Oracle DBA with over 20 years of IT experience. He has built and managed cluster databases on about each and every platform that Oracle ever supported, from the famous OPS databases in version 7 to the latest RAC releases, currently being 11g. Ronald is constantly looking for ways to get the most out of the database to make the investment for the customers even more valuable. He has a great knowledge of how to handle the power of the rich Unix environment, which makes him a first class troubleshooter and solution architect. Next to his many spoken languages such as Dutch, English, German, and French, he also writes fluently in many scripting languages.
Currently Ronald is a principal consultant working for Ciber in The Netherlands where he cooperates in many complex projects for large companies where downtime is not an option. Ciber (CBR) is one of the few Oracle Partners on the Diamond level.
Ronald often replies on the Oracle forums, writes his own blog (http://ronr.blogspot.com) called 'from errors we learn', and writes for various Oracle-related magazines. He has also authored a book, Mastering Oracle Scheduler in Oracle 11g Databases, where he fills the gap between the Oracle Documentation and the customers' questions.
Ronald has lots of certifications, among them:
Ronald fills his time with Oracle, his family, sky-diving, radio-controlled model airplane flying, running a scouting group, and having a lot of fun.
His quote is: "a problem is merely a challenge that might take a little time to solve".
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I dedicate this book to my friends, family, colleagues, and all of the Oracle database professionals who work long and hard over weekends, nights, and holidays to keep their database systems online and running smoothly.
--Ben PrusinskiI would like to dedicate this book to my parents Mr. and Mrs. Saifulla.
--Syed Jaffer HussainPreface
Oracle Real Application Clusters, or Oracle RAC for short (formerly known as Oracle Parallel Server), is a clustering technology that provides the ability to scale performance and improve server availability for Oracle data center environments. Oracle RAC not only serves as a part of the Oracle Maximum Availability Architecture (MAA) for disaster recovery purposes, but it's also used for other purposes such as scaling up and out for performance by adding additional nodes to an Oracle data center environment. However, getting started with Oracle RAC can be difficult and challenging for the Oracle professional who is new to this technology and has worked only with single-instance Oracle databases. This book provides the guidance needed to overcome that difficulty, covering the key features of Oracle RAC. Each chapter introduces new features, allowing you to develop competency in the administration of this advanced technology.
By the end of the book, you will not only have experimented with numerous examples, but you will have also deployed a complete Oracle RAC environment and solution.
What this book covers
Chapter 1, High Availability, serves as the most basic introduction to concepts of high availability with regard to how Oracle RAC comes into play. The chapter includes a comprehensive review of the core areas of high availability and disaster recovery as well as how the Oracle RAC technology fits into a strategy for implementing high availability. The chapter also includes a review of key Oracle technologies that complement Oracle RAC for a disaster recovery implementation.
Chapter 2, Oracle 11g RAC Architecture, provides a blueprint from concept to finish of how to design an Oracle 11g RAC environment from the hardware and storage layers to the software and database layers.
Chapter 3, Clusterware Installation, provides step-by-step instructions on how to install Oracle 11g RAC. The chapter explains all of the steps required for the installation of the Oracle 11g R1 RAC Clusterware and Oracle 11g R1 RDBMS binaries, as well as the latest 11g R2 RAC Clusterware (grid) and RDBMS binaries.
Chapter 4, Automatic Storage Management, discusses the key concepts for Oracle 11g Automatic Storage Management (ASM) technology and provides an overview of ASM features. For this chapter, we assume that you have already worked with the ASM Oracle database 10g environment.
Chapter 5, Managing and Troubleshooting Oracle 11g Clusterware, explains how to resolve complex problems with Oracle 11g RAC clusterware failures. We show you how to identify the root cause of Oracle Clusterware issues along with timely solutions based on case study methods.
Chapter 6, RAC Database Administration and Workload Management, provides a deep dive into various methods that are available to create and manage RAC databases. The workload management segment in this chapter further explains how your application can take advantage of running on the RAC database to improve overall performance and scalability. It also discusses most of the useful new features introduced in 11g R1 and 11g R2 versions.
Chapter 7, Backup and Recovery, shows you how to back up and recover the Oracle RAC environment using different approaches. In this chapter, the emphasis will be placed on backup and recovery using RMAN. However, we also briefly discuss the various methods along with the pros and cons of each of them. In addition, new features of RMAN within Oracle 11g R1 and 11g R2 along with OCR and voting disk backup and recovery are covered in great detail.
Chapter 8, Performance Tuning, first explains how the differences between an Oracle RAC cluster and a non-RAC single-instance Oracle database pose unique challenges to the Oracle database professional. This chapter will focus on how to tune a massively parallel Oracle RAC database, consisting of many instances residing on different nodes of a cluster and accessing the same disk files residing on shared disk storage.
Chapter 9, Oracle 11g Clusterware Upgrade, explains the pros and cons of an upgrade process as well as the possibilities during upgrade scenarios. We also demonstrate how to upgrade the Oracle 10g R2 clusterware to 11g R1 and then perform a second upgrade from 11g R1 to 11g R2 versions. Furthermore, we also explain how to downgrade Oracle Clusterware to a previous version.
Chapter 10, Real-world Scenarios, teaches you how to perform many common real-world business scenarios, such as adding and removing cluster nodes, as well as how to convert non-RAC Oracle databases to Oracle RAC and how to relocate an Oracle RAC database instance, which are key skills for an Oracle RAC database administrator.
Chapter 11, Enabling RAC for EBS, discusses how to implement RAC for the Oracle R12 E-Business Suite (EBS) environment. We look at the cases for why Oracle RAC would be suitable for an Oracle R12 EBS environment to achieve a scalable and resilient architecture.
Chapter 12, Maximum Availability, discusses the complete picture of solutions for Oracle to enable high availability and disaster recovery. A detailed explanation is provided of these key technologies, including Oracle Streams and Oracle Data Guard, and how they complement the Oracle 11g RAC environment. We then move into a few case studies that show you how to enable Data Guard and Streams for Oracle RAC environments.
Appendix, Additional Resources and Tools for the Oracle RAC Professional is a handy summary of beneficial My Oracle Support notes that can provide assistance for Oracle RAC environments.
What you need for this book
Oracle 11g RAC is a complex technology that demands many resources, from logistical to hardware, to implement. This means that you will need multiple servers and technical resources to be carefully orchestrated in order to achieve a successful RAC implementation. In a sense, the Oracle RAC architect is a symphony conductor who must skillfully place all of the key chess pieces into motion to avoid failure and delays with the deployment. As many DBAs have no prior RAC exposure, we gently introduce the basic concepts first, in order to familiarize you with RAC, before jumping into the deep ocean of RAC administration. Have no fear, while RAC is a complex beast, it can be tamed. The only prerequisite is to have at least a basic understanding of Oracle database concepts and Oracle database administration before learning about RAC. It is also useful to have access to a test or sandbox environment to install and configure an RAC environment with the examples in the book. Nothing beats hands-on experience.
Having an Internet connection and Oracle database server while reading is extremely useful as well. We also recommend that if you want a virtual environment to set up and play with RAC, then you consult the many whitepapers written by Dr. Tim Hall (http://oracle-base.com) that provide detailed step-by-step instructions on how to download, install, and configure an Oracle 11g RAC environment in both virtual server and standalone environments.
Who this book is for
If you are an Oracle DBA who wants to administer Real Application Clusters, then this book is for you. Basic understanding of Oracle DBA is required. No experience of RAC is required.
Conventions
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Tip
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Chapter 1. High Availability
High availability is a discipline within database technology that provides a solution to protect against data loss and against downtime, which is costly to mission-critical database systems. In this chapter, we will discuss how Oracle 11g RAC provides you with mission-critical options for minimizing outages and downtime as well as how RAC fits into the overall scheme for maintenance of a comprehensive disaster recovery and business continuity policy. In this chapter, we will provide you with an introduction to the high availability concepts and solutions that are workable for Oracle 11g. As such, we will provide details on what constitutes high availability and what does not. By having the proper framework, you will understand how to leverage Oracle RAC and auxiliary technologies including Oracle Data Guard to maximize the Return On Investment (ROI) for your data center environment. In summary, we will discuss the following topics:
High availability concepts
High availability provides data center environments that run mission-critical database applications with the resiliency to withstand failures that may occur due to natural, human, or environmental conditions. For example, if a hurricane wipes out the production data center that hosts a financial application's production database, high availability would provide the much-needed protection to avoid data loss, minimize downtime, and maximize availability of the firm's resources and database applications. Let's now move to the high availability concepts.
Planned versus unplanned downtime
The distinction needs to be made between planned downtime and unplanned downtime. In most cases, planned downtime is the result of maintenance that is disruptive to system operations and cannot be avoided with current system designs for a data center. An example of planned downtime would be a DBA maintenance activity such as database patching to an Oracle database, which would require taking an outage to take the system offline for a period of time. From the database administrator's perspective, planned downtime situations usually are the result of management-initiated events.
On the other hand, unplanned downtime issues frequently occur due to a physical event caused by a hardware, software, or environmental failure or caused by human error. A few examples of unplanned downtime events include hardware server component failures such as CPU, disk, or power outages.
Most data centers will exclude planned downtime from the high availability factor in terms of calculating the current total availability percentage. Even so, both planned and unplanned maintenance windows affect high availability. For instance, database upgrades require a few hours of downtime. Another example would be a SAN replacement. Such items make comprehensive four nine solutions nigh impossible to implement without additional considerations. The fact is that implementing a true 100% high availability is nearly impossible without exorbitant costs. To have complete high availability for all components within the data center requires an architecture for all systems and databases that eliminates any Single Point of Failure (SPOF) and allows for total online availability for all server hardware, network, operating systems, applications, and database systems.
Service Level Agreements for high availability
When it comes to determining high availability ratios, this is often expressed as the percentage of uptime in a given year. The following table shows the approximate downtime that is allowed for a specific percentage of high availability, granted that the system is required to operate continuously. Service Level Agreements (SLAs) usually refer to monthly downtime or availability in order to calculate service levels to match monthly financial cycles. The following table from the International Organization for Standardization (ISO) illustrates the correlation between a given availability percentage and the relevant amount of time a system would be unavailable per year, month, or week:
Availability %
Annual downtime
Monthly downtime*
Weekly downtime
90%
36.5 days
72 hours
16.8 hours
95%
18.25 days
36 hours
8.4 hours
98%
7.30 days
14.4 hours
3.36 hours
99%
3.65 days
7.20 hours
1.68 hours
99.5%
1.83 days
3.60 hours
50.4 minutes
99.8%
17.52 hours
86.23 minutes
20.16 minutes
99.9% ("three nines")
8.76 hours
43.2 minutes
10.1 minutes
99.95%
4.38 hours
21.56 minutes
5.04 minutes
99.99% ("four nines")
52.6 minutes
4.32 minutes
1.01 minutes
99.999% ("five nines")
5.26 minutes
25.9 seconds
6.05 seconds
99.9999% ("six nines")
31.5 seconds
2.59 seconds
0.605 seconds
Note
For monthly calculations, a 30-day month is used.
It should be noted that availability and uptimes are not the same thing. For instance, a database system may be online but not available, as in the case of application outages such as when a user's SQL script cannot be executed.
In most cases, the number of nines is not often used by the database or system professional when measuring high availability for data center environments because it is difficult to extrapolate such hard numbers without a large test environment. For practical purposes, availability is calculated more as a probability or average downtime given per annual basis.
High availability interpretations
When it comes to discussing how availability is measured, there is a debate on the correct method of interpretation for high availability ratios. For instance, an Oracle database server that has been online for 365 days in a given non-leap year might have been eclipsed by an application failure that lasted for nine hours during a peak usage period. As a consequence, the users will see the complete system as unavailable, whereas the Oracle database administrator will claim 100% "uptime." However, given the true definition of availability, the Oracle database will be approximately 99.897% available (8751 hours of available timeout of 8760 hours per non-leap year). Furthermore, Oracle database systems experiencing performance problems are often deemed partially or entirely unavailable by users, while in the eyes of the database administrator the system is fine and available.
Another situation that presents a challenge in terms of what constitutes availability would be the scenario in which the availability of a mission-critical application might go offline yet is not viewed as unavailable by the Oracle DBA, as the database instance could still be online and thus available. However, the application in question is offline to the end user, thus presenting a status of unavailable from the perspective of the end user. This illustrates the key point that a true availability measure must be from a holistic perspective and not strictly from the database's point of view.
Availability should be measured with comprehensive monitoring tools that are themselves highly available and present the proper instrumentation. If there is a lack of instrumentation, systems supporting high-volume transaction processing frequently during the day and night, such as credit-card-processing database servers, are often inherently better monitored than systems that experience a periodic lull in demand. Currently, custom scripts can be developed in conjunction with third-party tools to provide a measure of availability. One such tool that we recommend for monitoring database, server, and application availability is that provided by Oracle Grid Control, which also includes Oracle Enterprise Manager.
Oracle Grid Control provides instrumentation via agents and plugin modules to measure availability and performance on a system-wide enterprise level, thereby greatly aiding the Oracle database professional to measure, track, and report to management and users on the status of availability with all mission-critical applications and system components. However, the current version of Oracle Enterprise Manager will not provide a true picture of availability until 11g Grid Control is released in the future.
Recovery time and high availability
Recovery time is closely related to the concept of high availability. Recovery time varies based on system design and failure experienced, in that a full recovery may well be impossible if the system design prevents such recovery options. For example, if the data center is not designed correctly with the required system and database backups and a standby disaster recovery site in place, then a major catastrophe such as a fire or earthquake will almost always result in complete unavailability until a complete MAA solution is implemented. In this case, only a partial recovery may be possible. This drives home the point that for all major data center operations, you should always have a backup plan with an offsite secondary disaster-recovery data center to protect against losing all critical systems and data.
In terms of database administration for Oracle data centers, the concept of data availability is essential when dealing with recovery time and planning for highly available options. Data availability references the degree to which databases such as Oracle record and report transactions. Data management professionals often focus just on data availability in order to judge what constitutes an acceptable data loss with different types of failure events. While application service interruptions are inconvenient and sometimes permitted, data loss is not to be tolerated. As one Chief Information Officer (CIO) and executive once told us while working for a large financial brokerage, you can have the system down to perform maintenance but never ever lose my data!
The next item related to high availability and recovery standards is that of Service Level Agreements or SLAs for data center operations. The purpose of the Service Level Agreement is to actualize the availability objectives and requirements for a data center environment per business requirements into a standard corporate information technology (IT) policy.
System design for high availability
Ironically, by adding further components to the overall system and database architecture design, you may actually undermine your efforts to achieve true high availability for your Oracle data center environment. The reason for this is by their very nature, complex systems inherently have more potential failure points and thus are more difficult to implement properly. The most highly available systems for Oracle adhere to a simple design pattern that makes use of a single, high quality, multipurpose physical system with comprehensive internal redundancy running all interdependent functions, paired with a second like system at a separate physical location. An example would be to have a primary Oracle RAC clustered site with a second Disaster Recovery site at another location with Oracle Data Guard and perhaps dual Oracle RAC clusters at both sites connected by stretch clusters. The best possible way to implement an active standby site with Oracle would be to have Oracle Streams and Oracle Data Guard. Large commercial banking and insurance institutions would benefit from this model for Oracle data center design to maximize system availability.
Business Continuity and high availability
Business Continuity Planning (BCP) refers to the creation and validation of a rehearsed operations plan for the IT organization that explains the procedures of how the data center and business unit will recover and restore, partially or completely, interrupted business functions within a predetermined time after a major disaster.
In its simplest terms, BCP is the foundation for the IT data center operations team to maintain critical systems in the event of disaster. Major incidents could include events such as fires, earthquakes, or national acts of terrorism.
BCP may also encompass corporate training efforts to help reduce operational risk factors associated with the lack of information technology (IT) management controls. These BCP processes may also be integrated with IT standards and practices to improve security and corporate risk management practices. An example would be to implement BCP controls as part of Sarbanes-Oxley (SOX) compliance requirements for publicly traded corporations.
The origins for BCP standards arose from the British Standards Institution (BSI) in 2006 when the BSI released a new independent standard for business continuity named BS 25999-1. Prior to the introduction of this standard for BCP, IT professionals had to rely on the previous BSI information security standard, BS 7799, which provided only limited standards for business continuity compliance procedures. One of the key benefits of these new standards was to extend additional practices for business continuity to a wider variety of organizations, to cover needs for public sector, government, non-profit, and private corporations.
Disaster Recovery
Disaster Recovery (DR) is the process, policies, and procedures related to preparing for recovery or continuation of technology infrastructure critical to an organization after either a natural or human-caused disaster.
Disaster Recovery Planning (DRP) is a subset of larger processes such as Business Continuity and should include planning for resumption of applications, databases, hardware, networking, and other IT infrastructure components. A Business Continuity Plan includes planning for non-IT-related aspects, such as staff member activities, during a major disaster as well as site facility operations, and it should reference the Disaster Recovery Plan for IT-related infrastructure recovery and business continuity procedures and guidelines.
Business Continuity and Disaster Recovery guidelines
The following recommendations will provide you with a blueprint to formulate your requirements and implementation for a robust Business Continuity and Disaster Recovery plan:
The first step enables you to define the scope of your new Business Continuity Plan. It provides you with an idea of the limitations and boundaries of the Business Continuity Plan. It also includes important audit and risk analysis reports for corporate assets.
Conducting a Business Impact Analysis session:Business Impact Analysis (BIA) is the assessment of financial losses to institutions, which usually results as the consequence of destructive events such as the loss or unavailability of mission-critical business services.
Obtaining support for your business continuity plans and goals from the executive management team:You will need to convince senior management to approve your business continuity plan, so that you can flawlessly execute your disaster recovery planning. Assign stakeholders as representatives on the project planning committee team, once approval is obtained from the corporate executive team.
Understanding its specific role:In the possible event of a major disaster, each of your departments must be prepared to take immediate action. In order to successfully recover your mission-critical database systems with minimal loss, each team must understand the BCP and DRP plans, as well as follow them correctly. Furthermore, it is also important to maintain your DRP and BCP plans, as well as conduct periodic training of your IT staff members on a regular basis to have successful response time for emergencies. Such "smoke tests" to train and keep your IT staff members up to date on the correct procedures and communications will pay major dividends in the event of an unforeseen disaster.
One useful tool for creating and managing BCP plans is available from the National Institute of Standards and Technologies (NIST). The NIST documentation can be used to generate templates that can be used as an excellent starting point for your Business Continuity and Disaster Recovery planning. We highly recommend that you download and review the following NIST publication for creating and evaluating BCP plans, Contingency Planning Guide for Information Technology Systems, which is available online at http://csrc.nist.gov/publications/nistpubs/800-34/sp800-34.pdf.
Additional NIST documents may also provide insight into how best to manage new or current BCP or DRP plans. A complete listing of NIST publications is available online at http://csrc.nist.gov/publications/PubsSPs.html.
Fault-tolerant systems and high availability
Fault tolerance is data center technology that enables a system to continue to function correctly in the face of a failure with one or more faults within any given key component of the system architecture or data center. If operating quality experiences major degradation, the decrease in functionality of the environment is usually in direct proportion to the severity of the failure, whereas a poorly designed system will completely fail and breakdown with a small failure. In other words, fault tolerance gives you that added layer of protection and support to avoid a total meltdown of your mission-critical data center and, in our case, Oracle servers and database systems. Fault tolerance is often associated with highly available systems such as those found with Oracle Data Guard and Oracle RAC technologies.
Data formats may also be designed to degrade gracefully. For example, in the case of Oracle RAC environments, services provide for load balancing to minimize performance issues in the event that one or more nodes in the cluster are lost due to an unforeseen event.
Recovery from errors in fault-tolerant systems provides for either rollforward or rollback operations. For instance, whenever the Oracle server detects that it has an error condition and cannot find data from a missed transaction, rollback will occur either at the instance level or application level (a transaction must be atomic in that all elements must commit or rollback). Oracle takes the system state at that time and rolls back transactional changes to be able to move forward. Whenever a rollback is required for a transaction within Oracle, Oracle reverts the system state to some earlier correct version—for example, using the database checkpoint and rollback process inherent in the Oracle database engine and moving forward from there.
Rollback recovery requires that the operations between the checkpoint (implicit checkpoints are NEVER required for transactional recovery) and the detected erroneous state can be made to be transparent. Some systems make use of both rollforward and rollback recovery for different errors or different parts of one error.
For Oracle, database recovery always rolls back failed transactions and restores the state of the rollback or undo, from which it then rolls forward using the contents of the rollback or undo segments. However, when it comes to transactional-based recovery, Oracle only rolls back. Within the scope of an individual system, fault tolerance can be achieved by anticipating exceptional conditions and building the system to cope with them, and in general, aiming for self-healing so that the system converges towards an error-free state. In any case, if the consequence of a system failure is catastrophic, the system must be able to use reversion to fall back to a safe mode. This is similar to rollback recovery but can be a human action if humans are present in the loop.
Requirements for implementing fault tolerance
The basic characteristics of fault tolerance are:
In addition, fault-tolerant systems are characterized in terms of both planned and unplanned service outages. These are usually measured at the application level and not just at a hardware level. The figure of merit is called availability and is expressed as a percentage. For instance, a five nine system would therefore statistically provide 99.999% availability. Fault-tolerant systems are typically based on the concept of redundancy. In theory, this would be ideal; however, in reality this is an elusive impractical goal. Due to the time required to fail over, reestablish middle-tier connections, and perform application restarts, it is not realistic to have complete availability. We can obtain four nines as the best goal for high availability with Oracle systems. For Oracle RAC, you can deploy a fault-tolerant environment by using multiple network interface cards, dual Host Bus Adapters (HBAs), and multiple switches to avoid any Single Point of Failure.
Fault tolerance and replication
By using spare components, we address the first fundamental characteristic of fault tolerance in the following two ways:
At the storage layer, the major implementations of RAID (Redundant Array of Independent Disks) with the exception of disk striping (RAID 0) provide you with fault-tolerant appliances that also use data redundancy.
Bringing the replications into synchrony requires making their internal stored states the same. They can be started from a fixed initial state such as the reset state. Alternatively, the internal state of one replica can be copied to another replica.
One variant of Data Mirror Replication (DMR) is pair-and-spare. Two replicated elements operate in lockstep as a pair, with a voting circuit that detects any mismatch between their operations and outputs a signal indicating that there is an error. Another pair operates exactly the same way. A final circuit selects the output of the pair that does not proclaim that it is in error. Pair-and-spare requires four replicas rather than the three of DMR, but has been used commercially.
If a system experiences a failure, it must continue to operate without interruption during the repair process.
When a failure occurs, the system must be able to isolate the failure to the offending component. This requires the addition of dedicated failure-detection mechanisms that exist only for the purpose of fault isolation.
Recovery from a fault condition requires classifying the fault or failing component. The National Institute of Standards and Technology (NIST) categorizes faults based on locality, cause, duration, and effect.
