Module 7

Implementing High Availability

Module Overview

• Overview of High Availability Options

• Configuring Highly Available Mailbox Databases

• Deploying Highly Available Non-Mailbox Servers

Lesson 1: Overview of High Availability Options

• What Is High Availability?

• Discussion: Components of a High Availability Solution

• High Availability Solution for Mailbox Servers

• High Availability Solution for Non-Mailbox Servers

What Is High Availability?

High availability:

• Implements system design that ensures a high level of operational continuity

• Is measured by the percentage of time the application is available

Availability Target Permitted Annual Downtime

99% 87 hours, 36 minutes

99.9% 8 hours, 46 minutes

99.99% 52 minutes, 34 seconds

99.999% 5 minutes, 15 seconds

Discussion: Components of a High Availability Solution

• Which components are important for running a high availability solution?

• What are some single points of failure in a messaging solution?

High Availability Solution for Mailbox Servers

Mailbox data high availability:

• Single database failover

• Requires failover clustering feature

• Allows up to 16 copies of each database

• Allows up to 14 days for lag copies

Public Folder high availability:

• Leverages Public Folder replication

• Is similar to previous Exchange Server versions

High Availability Solution for Non-Mailbox Servers

Server Role High Availability Solutions

Client Access • Deploy multiple servers

• Create a client access array

• Implement network load balancing

Hub Transport • Deploy multiple servers in each site

Edge Transport • Deploy multiple servers

• Implement multiple MX records or round-robin DNS

Unified Messaging

• Deploy multiple servers

Lesson 2: Configuring Highly Available Mailbox Databases

• What Is a Database Availability Group?

• What Is Active Manager?

• What Is Continuous Replication?

• How Are Databases Protected in a DAG?

• Comparing Exchange Server 2010 to Exchange Server 2007 Mailbox Availability Options

• Configuring Databases for High Availability

• Demonstration: How to Create and Configure a DAG

• What Is the Transport Dumpster?

• Understanding the Failover Process

• Demonstration: How to Monitor Replication Health

What Is a Database Availability Group?

A DAG is a collection of servers that provides the infrastructure for replicating and activating database copies. DAGs:

• Require the failover clustering feature, although all installation and configuration is done with the Exchange Server management tools

• Use Active Manager to control failover

• Use an enhanced version of the continuous replication technology that Exchange Server 2007 introduced

• Can be created after the Mailbox server is installed

• Allow a single database to be activated on another server in the group without affecting other databases

• Allow up to 16 copies of a single database on separate servers

• Define the boundary for replication

What Is Active Manager?

Active Manager:

• Runs a process on each server in the DAG

• One node is the Primary Active Manager

• Remaining nodes are Secondary Active Managers

• Manages which database copies are active and which are passive

• Stores database state information

• Manages database switchover and failover processes

• Does not require direct administration configuration

What Is Continuous Replication?

Database Availability GroupDatabase Availability Group

DB1DB1 DB1DB1 DB1DB1

How Are Databases Protected in a DAG?

DB4DB4

DB2DB2

DB3DB3

DB1DB1

DB2DB2

DB4DB4 DB4DB4

DB2DB2

DB3DB3

Continuous replication protects databases across servers in the DAGContinuous replication protects databases across servers in the DAG

Comparing Exchange Server 2010 to Exchange Server 2007 Mailbox Availability Options

Exchange Server 2007 Exchange Server 2010

LCR CCR SCR SCC DAG

Point of Failure

Server None None Storage None

VSS Backup Supported Supported Not supported

Supported Supported

Replication Copies

Single copy on server

Single copy on passive node

Multiple targets

None Up to 16 targets

Log Replay Delay

None None Up to 24 hours or 50 log files

None Up to 14 days

Data Loss Protection

Transport dumpster

Transport dumpster

Not available

None Transport dumpster

Failover Manual Automatic failover

Manual Automatic failover

Automatic switchover by database

Can Run with Multiple Roles

Yes No Target Only

No Yes

Configuring Databases for High Availability

After creating a DAG, adding Mailbox servers to the DAG, and configuring the DAG, you must still do the following:

• Create database copies

• Set truncation lag time

• Set replay lag time

• Set preferred list sequence number

Demonstration: How to Create and Configure a DAG

In this demonstration, you will see how to create and configure a DAG

What Is the Transport Dumpster?

The transport dumpster:

• Protects against Mailbox server failures when transaction logs have been lost

• Keeps copies of all messages delivered in the transport queue (mail.que) until the transaction logs have replicated to all servers in the DAG, or until the maximum dumpster size is reached

• Redelivers missing e-mail messages when a failure occurs

Understanding the Failover Process

If a failure occurs, the following steps occur for the failed database:

Active Manager determines the best copy to activate

The replication service on the target server attempts to copy missing log files from the best “source”:• If successful, the database mounts with zero data loss• If unsuccessful (failover), the database mounts based on

the AutoDatabaseMountDial setting

The mounted database generates new log files (using the same log generation sequence)

Transport dumpster requests are initiated for the mounted database to recover lost messages

When original server or database recovers, it determines if any logs are missing or corrupt, and fixes them if possible

Demonstration: How to Monitor Replication Health

In this demonstration, you will see how to:

• Monitor replication health using the Exchange Management Console and the Exchange Management Shell

• View various status messages

• View available statistics

Lesson 3: Deploying Highly Available Non-Mailbox Servers

• How High Availability Works for Client Access Servers

• How Shadow Redundancy Provides High Availability for Hub Transport Servers

• How High Availability Works for Edge Transport Servers

How High Availability Works for Client Access Servers

A client access array is created with multiple Client Access servers. You can achieve high availability and load balancing by using one of these methods:

• Network load balancing

• Hardware-based load balancing

• Round-robin DNS

Transport server delays message deletion until it verifies that the message has been delivered past the next hop

How Shadow Redundancy Provides High Availability for Hub Transport Servers

HubHub

External SMTP Mail

Server

External SMTP Mail

Server

Edge2Edge2

Edge1Edge1

How High Availability Works for Edge Transport Servers

Load balancing and high availability methods for Edge Transportinclude:

• Multiple DNS MX records that are created to specify multiple authoritative SMTP servers for the domain.

• Hardware-based load balancing that is used to load balance inbound SMTP connections to any available Edge Transport server.

Load balancing and high availability methods for Edge Transportinclude:

• Multiple DNS MX records that are created to specify multiple authoritative SMTP servers for the domain

• Hardware-based load balancing that is used to load balance inbound SMTP connections to any available Edge Transport server

Lab: Implementing High Availability

• Exercise 1: Deploying a DAG

• Exercise 2: Deploying Highly Available Hub Transport and Client Access Servers

• Exercise 3: Testing the High Availability Configuration

Logon information

Estimated time: 60 minutes

Virtual machines

10135A-VAN-DC1 10135A-VAN-EX1 10135A-VAN-EX2 10135A-VAN-EX3

User name Administrator

Password Pa$$w0rd

Lab Scenario

You are the messaging administrator for A. Datum Corporation. You have completed the basic installation for three Exchange servers. Now you must complete the configuration so that they are highly available.

Lab Review

• When might you choose to initiate a database switchover?

• If you deploy only two Hub Transport servers in an Active Directory site, would shadow redundancy protect messages between mailboxes in the same site?

Module Review and Takeaways

• Review Questions

• Common Issues and Troubleshooting Tips

• Real-World Issues and Scenarios

• Best Practices