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Professional SQL Server High Availability and Disaster Recovery

You're reading from   Professional SQL Server High Availability and Disaster Recovery Implement tried-and-true high availability and disaster recovery solutions with SQL Server

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Product type Paperback
Published in Jan 2019
Publisher Packt
ISBN-13 9781789802597
Length 564 pages
Edition 1st Edition
Languages
Concepts
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Author (1):
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Ahmad Osama Ahmad Osama
Author Profile Icon Ahmad Osama
Ahmad Osama
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Toc

Table of Contents (24) Chapters Close

About the Book
About the Authors
Objectives
Audience
Approach
Hardware Requirements
Software Requirements
Conventions
Installation
Installing the Code Bundle
Additional Resources
1. Lesson 1 FREE CHAPTER
2. Getting Started with SQL Server HA and DR 3. Lesson 2
4. Transactional Replication 5. Lesson 3
6. Monitoring Transactional Replication 7. Lesson 4
8. AlwaysOn Availability Groups 9. Lesson 5
10. Managing AlwaysOn Availability Groups 11. Lesson 6
12. Configuring and Managing Log Shipping 1. Appendix

HA and DR Terminologies

The following terms are important in the world of HA and DR so that you can correctly choose the best possible HA and DR solutions and for the better understanding of HA and DR concepts.

Availability

Availability or uptime is defined as the percentage that a system or an application should be available for in a given year. Availability is expressed as Number of Nines.

For example, a 90%, one nine, availability means that a system can tolerate a downtime of 36.5 hours in a year, and a 99.999%, five nines, availability means that a system can tolerate a downtime of 5.26 minutes per year.

The following table, taken from https://en.wikipedia.org/wiki/High_availability, describes the availability percentages and the downtime for each percentage:

Note

This link also talks about how this is calculated. You can look at it, but a discussion on calculation is out of the scope of this book.

Figure 1.4: Availability table
Figure 1.4: Availability table

In the preceding table, you can see that as...

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