Oracle Consulting Oracle Training Development

Remote DBA

Remote DBA Plans  

Remote DBA Service

Remote DBA RAC

Remote DBA Oracle Home
Remote DBA Oracle Training
Remote DBA SQL Tuning Consulting
Remote DBA Oracle Tuning Consulting
Remote DBA Data Warehouse Consulting
Remote DBA Oracle Project Management
Remote DBA Oracle Security Assessment
Remote DBA Unix Consulting
Burleson Books
Burleson Articles
Burleson Web Courses
Burleson Qualifications
Oracle Links
Remote DBA Oracle Monitoring
Remote DBA Support Benefits
Remote DBA Plans & Prices
Our Automation Strategy
What We Monitor
Oracle Apps Support
Print Our Brochure
Contact Us (e-mail)
Oracle Job Opportunities
Oracle Consulting Prices





Remote DBA services

Remote DBA Support

Remote DBA RAC

Remote DBA Reasons

Remote Oracle Tuning

Remote DBA Links

Oracle DBA Support

Oracle DBA Forum

Oracle Disaster

Oracle Training

Oracle Tuning

Oracle Training

 Remote DBA SQL Server

Remote MSSQL Consulting

Oracle DBA Hosting

Oracle License Negotiation







 Oracle 11g High Availability Database
Oracle Tips by Burleson Consulting

Oracle 11g Grid & Real Application Clusters by Rampant TechPress is written by four of the top Oracle database experts (Steve Karam, Bryan Jones, Mike Ault and Madhu Tumma).  The following is an excerpt from the book.

The Need for Highly Available Data

Unplanned downtime and planned downtime are costly in terms of lost revenue and time.  Planned downtime in one time zone has a direct impact on the business hours of another time zone.


It is important to understand certain key terms and concepts before examining HA systems and databases.


Failure is defined as a departure from expected behavior on an individual computer system.  Software, hardware, operator and procedural errors, along with environmental factors, can each cause a system failure. 


Availability is a measure of the amount of time a system or component performs its specified function. Availability is related to, but differs from, reliability. Reliability measures how frequently the system fails; availability measures the percentage of time the system is in its operational state.


To calculate availability, both the Mean Time Between Failures (MTBF) and the Mean Time To Recovery (MTTR) need to be known. The MTTR is a measure of how long, on average, it takes to restore the system to its operational state after a failure. If both the MTBF and the MTTR are known, availability can be calculated using the following formula:


Availability = MTBF / (MTBF + MTTR)


For example, if the data center fails roughly every six months (MTBF = six months) and it takes 20 minutes, on average, to return the data center to its operational state (MTTR = 20 minutes), then the data center availability is:


Availability = 6 months / (6 months + 20 minutes) = 99.992 percent.


Therefore, there are two ways to improve the availability of the system: increase MTBF or reduce MTTR. Having realized that system failures do occur or are unavoidable, system and database administrators need to focus on designing a reliable system with redundant components, as well as setting up reliable recovery methodology for when system failures happen.


Reliability is the starting point for building increasingly available systems since a measure of system reliability is how long it has been up and/or how long it typically stays up between failures. The nature of the failure is not important — any failure affects the system’s overall availability. As presented in the previous section, MTBF is often considered an important metric with respect to measuring system reliability.

  • There are two primary means of achieving greater reliability:

  • Building high MTBF components into the system

  • Adding MTBF components in redundant (N+1) configurations


Serviceability defines the time it takes to isolate and repair a fault or, more succinctly, the time it takes to restore a system to service following a failure. Mean Time To Recovery, or MTTR, is considered an important metric when discussing the serviceability of a system or some component of the system. MTTR, however, is a unit of time and does not factor into the cost of service.

Fault-Tolerant Systems

Another important distinction that needs to be made is between a high availability (HA) system and a fault tolerant (FT) system. Fault tolerant systems offer a higher level of resilience and recovery. They use a high degree of hardware redundancy and specialized software to provide near-instantaneous recovery from any single hardware or software unit failure.

Database Availability

When referring to the availability of databases, the total environment and infrastructure in which a typical database is located needs to be examined.  The database application has its own availability features that are unique from the system availability point of view.


There are three situations that need to be considered:

  • database server availability

  • network availability

  • disk storage availability and connectivity

Another important issue relevant for the database is the need to maintain the database consistency. Unlike application servers or other application instances, multiple database instances or copies of databases cannot exist. As the database contents change in real-time, multiple copies cannot be maintained in a timely manner.


Remote DBA Service

Oracle Tuning Book


Advance SQL Tuning Book 

BC Oracle support

Oracle books by Rampant

Oracle monitoring software










BC Remote Oracle Support

Remote DBA

Remote DBA Services

Copyright © 1996 -  2013 by Burleson. All rights reserved.

Oracle® is the registered trademark of Oracle Corporation.