What is a cluster – a definition!
A cluster is a group of computers, called nodes that function as a single computer/system to provide high availability and high fault tolerance for applications or services. Windows 2003 Servers can participate in a cluster configuration through the use of Cluster Services. If one member of the cluster (the node) is unavailable, the other computers carry the load so that applications or services are always (with a small interruption) available.
All nodes of the cluster use a Shared Disk – an external disk or disk subsystem which is accessible for all nodes through SCSI (2 Nodes) or Fibre Channel (more than 2 nodes). All data will be stored on the shared disk or an external disk subsystem (for example Exchange databases).
Every node has a local Exchange 2003 installation with a unique configuration for every cluster node. Each Cluster with Exchange 2003 has at a minimum one Exchange Virtual Server (EVS). An EVS is the logical node that will be used for all cluster operations. An EVS contains an IP address, network name, physical disk and an application.
A cluster can be …
- Active/Active or
- Active/Passive
Microsoft recommends only Active/Passive clusters – I will give you the reason later.
The number of cluster nodes supported by Windows 2003 Enterprise and Datacenter is 8 nodes. Windows Server 2003 Standard and Web Editon doesn’t support a Cluster.
In an Active/Passive cluster - If one node in the cluster fails, the active cluster failover to another node which becomes Active. This is called
Failover. If the failed node is back online, a
Failback can be manually initiated or automatically configured in the Cluster Group properties.
Every cluster node must have two network interfaces. One network interface for the cluster communication called the
private LAN and one network interface called the
public LAN. You can link a cluster with two nodes with a simple cross link cable. If more than two nodes exist in the cluster you have to use a dedicated switch / hub.
The private NIC is used for the Heartbeat communication (Cluster communication). A Heartbeat is much like a ping which can be used to test if the other cluster node is still available. If the heartbeat fails, the Failover process occurs.
Clustering changes with Exchange 2003 SP1
In versions before Exchange 2003 SP1, regardless of the number of cluster nodes you could only have one instance of a Public Folder store that is associated with the MAPI folder tree.
In Exchange 2003 SP1, the Exchange development team added the ability to have multiple MAPI Public Folder databases on a single multi node cluster.
This support was added because the Exchange team saw that Outlook 2003 cached mode puts a greater load on Public Folders like the Outlook Address Book (the OAB will be loaded offline at the client). With the help of multiple Public Folder stores the load can be spread across these folders. This allows a better client performance.
Why Active/Active cluster is not recommended
Active / Active cluster is not recommended because of Virtual memory (VM) fragmentation.
When two instances of the information store is running in one memory space, it might be possible that sufficient VM does not exist to bring the resource online during a failover/failback.
For more information see here:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;816893
There are three main concepts which reduce virtual memory fragmentation:
- Decrease the number of dynamic allocations when the system is started
- Increase the size of the virtual address space
- Allocate similar size allocations from common regions of memory
Exchange Server 2003 Cluster Requirements
- Microsoft Windows 2000 Advanced Server (up to two nodes)
- Windows 2000 Datacenter Server (up to four nodes)
- Windows 2000 must have SP3 + 329938 hotfix or SP4
- Windows Server 2003, Enterprise Edition (up to eight cluster nodes)
- Windows Server 2003, Datacenter Edition (up to eight cluster nodes)
- Hardware on cluster HCL
- Windows 2000 - Check lists for cluster service installation
http://go.microsoft.com/fwlink/?LinkId=266
- Windows Server 2003 – http://go.microsoft.com/fwlink/?LinkId=17219
- Microsoft Distributed Transaction Coordinator (MSDTC) installed
Exchange Server 2003 Cluster Setup Changes
- Block removal of node if an EVS is running on the cluster
- The /disasterrecovery switched is blocked
- Prevent Exchange 2003 from being first non-legacy server in a Exchange 5.5 site
- By default, POP3 and IMAP4 resource not created (as part of the Trustworthy Computing initiative from Microsoft)
- Cluster service account doesn’t requires Exchange full admin rights
- IPSEC is now supported between front-end servers and back-end clusters
Exchange Server 2003 Cluster Disk Changes
Windows 2003 clusters now support Volume Mount points to overcome the limits of traditional drive letter assignments. This new feature is very useful for four and eight node Exchange clusters because the traditional drive letter assignment in Exchange was very limited in cluster environments when multiple storage groups and stores where used.
Windows 2003 Cluster Setup
I will not explain every step for installing a Windows 2003 Cluster. For detailed information click the following
link.
I will show you only a few pictures.
Figure 1: Create a new Cluster
The Windows 2003 Cluster administrator after successful installation.
Figure 2: Cluster Administrator
Follow the Link for continuation
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