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The Windows Server Failover Clustering feature supports a certain maximum number of servers in a cluster. Servers in a

Failover Cluster are also called nodes. The maximum number of nodes varies depending on the version of the operating

system.

The following table outlines the maximum number of nodes that are supported in a cluster and the required shared disk

configuration.

Operating System Number of nodes

Storage

Windows NT 4.0 Enterprise EditionWindows 2000 Advanced ServerWindows 2000 Datacenter ServerWindows Server 2003, Enterprise EditionWindows Server 2003, Enterprise x64 Edition

Windows Server 2003, Datacenter EditionWindows Server 2003, Datacenter x64 Edition

1-2 SCSI

Windows NT 4.0 Enterprise EditionWindows 2000 Advanced Server

1-2 Fibre Channel

Windows 2000 Datacenter Server 1-4 Fibre Channel

Windows Server 2003, Enterprise EditionWindows Server 2003, Enterprise x64 EditionWindows Server 2003, Enterprise Edition forItanium-based Systems

Windows Server 2003, Datacenter EditionWindows Server 2003, Datacenter x64 EditionWindows Server 2003, Datacenter Edition forItanium-based SystemsWindows Server 2008, Enterprise EditionWindows Server 2008, Enterprise Edition forItanium-based SystemsWindows Server 2008, Datacenter EditionWindows Server 2008, Datacenter Edition forItanium-based Systems

1-8 Fibre Channel, iSCSI,or SAS

Windows Server 2008, Enterprise x64 EditionWindows Server 2008, Datacenter x64 EditionWindows Server 2008 R2 EnterpriseWindows Server 2008 R2 DatacenterMicrosoft Hyper-V Server 2008 R2

1-16 Fibre Channel, iSCSI,or SAS

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What does a failover cluster do?

A failover cluster is a group of independent computers that work together to increase the availability of applications and services. The clustered servers (called nodes) are connected by physical cables and bysoftware. If one of the cluster nodes fails, another node begins to provide service (a process known as

failover). Users experience a minimum of disruptions in service.

Who will be interested in failover clustering?

Failover clusters are used by IT professionals who need to provide high availability for services orapplications.

Are there any special considerations?

Microsoft supports a failover cluster solution only if all the hardware components are marked as "Certified

for Windows Server 2008 R2." In addition, the complete configuration (servers, network, and storage)must pass all tests in the Validate a Configuration wizard, which is included in the Failover ClusterManager snap-in.

Note that this policy differs from the support policy for server clusters in Windows Server 2003, whichrequired the entire cluster solution to be listed in the Windows Server Catalog under Cluster Solutions.

What new functionality does failover clustering provide?

Windows PowerShell cmdlets for failover clusters . Windows PowerShell is a new command-lineshell and scripting technology that uses consistent syntax and naming patterns across the roles andfeatures in Windows Server 2008 R2. The new cmdlets for failover clusters provide powerful ways toscript cluster configuration and management tasks. Windows PowerShell cmdlets will eventuallyreplace the Cluster.exe command-line interface.

If you use the Server Core installation option of Windows Server 2008 R2 for your failover cluster,the Windows PowerShell cmdlets for failover clusters simplify the local management of the cluster.

Read-only permissions option . You can assign read-only permission to a user or group whomight need to see the cluster but not change the configuration of the cluster.

Cluster Shared Volumes . With Cluster Shared Volumes, the configuration of clustered virtual

machines (supported by the Hyper-V feature) is much simpler than before. With Cluster SharedVolumes:

You can reduce the number of LUNs (disks) required for your virtual machines, instead of having to manage one LUN per virtual machine. (Previously, the recommendedconfiguration was one LUN per virtual machine, because the LUN was the unit of failover.)Many virtual machines can use a single LUN and can fail over without causing the othervirtual machines on the same LUN to also fail over.

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You can make better use of disk space, because you do not need to place each Virtual HardDisk (VHD) file on a separate disk with extra free space set aside just for that VHD file.Instead, the free space on a Cluster Shared Volume can be used by any VHD file on thatLUN.

You can more easily track the paths to VHD files and other files used by virtual machines.You can specify the path names, instead of identifying disks by drive letters (limited to thenumber of letters in the alphabet) or identifiers called GUIDs (which are hard to use andremember). With Cluster Shared Volumes, the path appears to be on the system drive of thenode, under the \ClusterStorage folder. However, this path is the same when viewed fromany node in the cluster.

If you use a few Cluster Shared Volumes to create a configuration that supports manyclustered virtual machines, you can perform validation more quickly than you could with aconfiguration that uses many LUNs to support many clustered virtual machines. With fewerLUNs, validation runs more quickly. (You perform validation by running the Validate aConfiguration Wizard in the snap-in for failover clusters.)

There are no special hardware requirements beyond what is already required for storage in afailover cluster (although Cluster Shared Volumes require NTFS).

Resiliency is increased, because the cluster can respond correctly even if connectivitybetween one node and the SAN is interrupted, or part of a network is down. The cluster willre-route the Cluster Shared Volumes traffic through an intact part of the SAN or network.

What existing functionality is changing?

Which editions include failover clustering?

The failover cluster feature is available in Windows Server 2008 R2 Enterprise and WindowsServer 2008 R2 Datacenter. The feature is not available in Windows Web Server 2008 R2 or WindowsServer 2008 R2 Standard.