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Module 7Implementing 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 minutes99.9% 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 ServersServer 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
DNSUnified 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 Group
DB1 DB1 DB1
How Are Databases Protected in a DAG?
DB4
DB2
DB3
DB1
DB2
DB4 DB4
DB2
DB3
Continuous 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 DAGPoint 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 DAGIn 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 HealthIn 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 ServersA 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
Hub
External SMTP Mail
Server
Edge2
Edge1
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 machines10135A-VAN-DC1 10135A-VAN-EX1 10135A-VAN-EX2 10135A-VAN-EX3
User name Administrator Password Pa$$w0rd
Lab ScenarioYou 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