BCHAPTER 6MCTS SQL SERVER 2008 EXAM 432MANAGING HIGH AVAILABILITYEXAM OBJECTIVES IN THIS CHAPTER

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Chapter 6

MCTS SQL Server 2008

Exam 432

Managing High

Availability

Exam objectives in this chapter:

Defining High Availability

■

SQL High-Availability Options

Expandability

Exam objectives review:

˛ Summary of Exam Objectives

˛ Exam Objectives Fast Track

˛ Exam Objectives Frequently Asked Questions

˛ Self Test

˛ Self Test Quick Answer Key

Introduction

This chapter focuses on how high availability ensures that your application is always

available. High availability incorporates such technologies as clustering, log shipping,

and replication. These will all be covered in detail, along with the pros and cons

of each, in the following chapter. Clustering has improved in SQL 2008, and these

improvements are discussed in this chapter.

It’s important to have a good understanding of the differences between each

technology, as each has its own advantages and disadvantages.

Hot-add CPU support and hot-add memory support will also be explained in

this chapter.

We will also touch on fault tolerant disk subsystems, like RAID 5 and

mirroring. It’s important to understand the performance implications of using

different disk systems.

The basic definition of high availability is a solution that allows for a hardware or

software failure but continues to run. Simple high-availability solutions include

using redundant hard drives, redundant memory, or redundant CPUs in your server.

As you get into more advanced solutions you will have redundant servers to provide

redundancy in the event of a software problem on one of the servers. In this case

the backup server will take over for the failed server either manually or

automatically.

When you are dealing with redundant hard drives you have several options.

When you configure redundant hard drives you can create what is called a RAID

array—a Redundant Array of Inexpensive Disks (or Redundant Array of Independent

Disks). The exact array depends on the number of disks you have, the protection

level you want, and the performance that you want to get from the system.

All RAID levels require at least two disks, and some require three or four disks.

Each RAID level has its strengths and weaknesses. Understanding these strengths

and weaknesses is key in deciding which RAID level you should select.

RAID 0 (also called a stripe set) is where all the disks are written to at the same

time. The upside to this RAID level is that it is very fast, and you get the most

amount of storage for your money. The downside to this system is that there is no

redundancy. Because there is no redundancy in a RAID 0 array, if any disk in the

RAID array fails then all data on the RAID array is lost.

RAID 1 (also called a mirror set) is where you have two disks, and as data is

written to the first disk, it is also written to the second disk at the same time.