You work as the database administrator at Domain.com. The Domain.com network consists of a single Active Directory domain named Domain.com. All servers on the Domain.com network run Windows Server2003. The Domain.com network contains two member servers named Certkiller -SR15 and Certkiller -SR16, as well as a single SQL Server 2005 database server named Certkiller -DB01. Certkiller -DB01 hosts a database named CK_Projects that contains mission critical data.
You need to provide fault tolerance and improve the availability of the CK_Projects database. Your solution must provide zero down time and the highest level of recovery. You are unable to acquire any additional hardware. You verify the Certkiller -SR15 and Certkiller -SR16 exceeds the recommended hardware requirements for SQL Server 2005. You then install SQL Server 2005 on Certkiller -SR15 and Certkiller -SR16.
What should you do next?

A.
Configure the three SQL Server 2005 database servers in a failover cluster with two active nodes and one passive node.

B.
Configure the three SQL Server 2005 database servers in a failover cluster with three active nodes.

C.
Configure the three SQL Server 2005 database servers in a failback cluster with three nodes.

D.
Configure Certkiller -SR15 as a mirror server and Certkiller -SR16 as witness server.

Explanation:
You can use mirrored servers to ensure the highest level of data protection. When you implement a witness server you ensure automatic failover when one of the mirrored servers becomes unavailable. This ensures zero-down time.
Incorrect Answers:
A, B, C: Clustering would require additional hardware in the form of a shared external hard disk drive.
Reference:
Microsoft SQL Server 2005 Books Online (2006), Index: witness [SQL Server]