Ensuring High Availability with Microsoft Exchange Server.pdf

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Aelita.Exchange.01_
IT Pro SERIES
Books
High Availability with
Microsoft Exchange Server
By Jerry Cochran
Kieran McCorry
Evan Morris
Daragh Morrissey
Tony Redmond
Paul Robichaux
Ensuring
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i
Contents
By Tony Redmond
Understanding Clusters and How Exchange Operates in Them . . . . . . . . . . . . . . . . . . . 1
By Paul Robichaux
By Daragh Morrissey
1. Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3. Redundancy, Redundancy, Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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ii Ensuring High Availability with Microsoft Exchange Server
By Kieran McCorry
Juggling Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Better Backup and Restore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Chapter 4: Exchange Server 2003 and VSS:
By Jerry Cochran
Volume Snapshot and Volume Cloning Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Sidebar: Better Backup through Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Exchange 2003 Backups Using VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Exchange 2003 Recovery Using VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
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Chapter 1
Exchange Server 2003 Clusters
By Tony Redmond
The history of Microsoft Exchange Server clusters is one of peaks and valleys, with cycles of
enthusiasm generated by new releases followed by depression as the releases don’t work out so well
in practice. Exchange Server 5.5 first supported Windows clusters, but the clusters were expensive to
deploy and were limited to two nodes configured in an active-passive cluster. Exchange 2000 Server
promised clusters spanning as many as four active nodes. However, Microsoft has been forced to
rescind that promise and now requires you to maintain a passive node because of memory-
fragmentation problems. In addition, you can deploy four-node Exchange 2000 clusters on only
Windows 2000 Datacenter Server, so the solution is expensive. The net result is that clusters represent
a small percentage of the hundreds of thousands of Exchange servers deployed today. No one is
willing to say exactly how many clusters are in production, but anecdotal evidence suggests that
fewer than 2 percent of all the deployed Exchange servers are in clusters.
On the surface, clusters seem to be an extremely effective way to achieve high degrees of
robustness and reliability. Indeed, UNIX and OpenVMS administrators have been deploying clusters
for these reasons for years. So, why haven’t Windows administrators been deploying Exchange 2000
and Exchange 5.5 clusters? The reasons why include added complexity, Exchange components that
can’t run on clusters, the lack of third-party product availability, memory fragmentation, and high
costs.
For clusters to work well, the email application and the OS must join forces. Microsoft promised
better clusters with Windows Server 2003 and Exchange Server 2003, but has the company keep that
promise? To answer this question, you need to know how clusters work, how Exchange in general
operates in a cluster, how Exchange 2000 specifically operates in a cluster, and what improvements
Exchange 2003 offers.
Understanding Clusters and How Exchange Operates in Them
The process of setting up and configuring hardware and software for clusters is more complex than
that for standard servers. Clusters typically boast multiple NICs. You need at least one NIC for the
public network and one NIC for the cluster “heartbeat,” which is the network signal between nodes
that lets the nodes know that the cluster is alive and well. Clusters use shared storage instead of
direct-connected drives because services depend on being able to move data between nodes when
problems occur—and the services can’t move the data if the data is restricted to a specific server.
Managing clusters differs from managing standard servers. Instead of controlling the set of
services for Exchange or other applications through the Computer Management console, you manage
them through the Cluster Administrator console, which Figure 1 shows. In this example, Cluster
Administrator shows a set of Exchange services running on a cluster. The console shows the
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2 Ensuring High Availability with Microsoft Exchange Server
additional resources that combine to form an Exchange virtual server, such as the disks, IP address,
and network name.
Figure 1
Cluster Administrator console
The concept of virtual servers is crucial to clusters. Exchange runs on a cluster as one or more
virtual servers. Each virtual server represents the set of resources (e.g., disks, a network name, the
Store) that Exchange needs to provide services to users. Exchange virtual servers run on physical
nodes within the cluster. The virtual servers manage the data in mailbox and public stores, which are
gathered into storage groups (SGs). An SG is the basic unit of storage for Exchange clusters. If a
physical node fails and the cluster has to move work within the cluster, the cluster distributes the SGs
from the failed server to other nodes rather than moves individual stores. After the failover, the SGs
come under the control of the Exchange virtual server running on that physical node.
After you understand the basic concepts of clusters and how Exchange operates in clusters, you
have to face the fact that not all Exchange components can run on a cluster. The reason why is
simple. In some cases, the Exchange component is old and wasn’t designed to run on anything other
than a standard server. Because the component is old and perhaps not needed by the majority of
Exchange installations, Microsoft never upgraded the component to support clusters. In other cases,
the component is used only in specific circumstances (e.g., for interoperability between Exchange
2000 and Exchange 5.5 servers), so that component doesn’t need to support clusters in the long
term. Table 1 lists the optional Exchange components and the degree of cluster support for those
components.
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