Overview
Earlier Windows versions (such as Windows Server 2003) use Microsoft Cluster Service (MSCS) to provide clustering functions. Windows Server 2008 and later versions use Windows Server Failover Cluster (WSFC).
An MSCS cluster is a server group consisting of independent computers. Nodes in the cluster work together as a single system to ensure that key applications and resources are always available to clients. The clustering function enables users and administrators to manage nodes as a whole instead of independent computers.
WSFC server clustering software adds new functions on the basis of MSCS. The new functions include the validation wizard and GPT disks.
MSCS
An MSCS server cluster contains a maximum of eight nodes, and can be configured as either of the following clusters:
- Single-node cluster
- Single-quorum device cluster
- Multi-node cluster
Each cluster node is connected to one or multiple cluster storage devices. In most Windows Server 2003 Enterprise Edition or Windows Server 2003 Datacenter Edition versions, cluster storage devices can be iSCSI, SAS, parallel SCSI, and Fibre Channel devices.
Table 10-1 lists the maximum number of nodes supported by different operating systems.
Operating System |
Storage Type |
Max. Number of Nodes |
|---|---|---|
Windows Server 2003 Enterprise Edition or Windows Server 2003 Datacenter Edition Version: Windows Server 2003 Windows Server 2003 SP1 Windows Server 2003 R2 Platform: x86 and x64 (non Itanium) |
Parallel SCSI |
2 |
Windows Server 2003 Enterprise Edition or Windows Server 2003 Datacenter Edition Version: Windows Server 2003 Windows Server 2003 SP1 Windows Server 2003 R2 Platform: x86 and x64 (Itanium) |
Fiber Channel |
8 |
Windows Server 2003 Enterprise Edition or Windows Server 2003 Datacenter Edition Version: Windows Server 2003 SP1 Windows Server 2003 R2 Platform: x86 and x64 (Itanium) |
iSCSI or SAS |
8 |
WSFC
A WSFC cluster is a group of independent servers that work together to improve the availability of applications and services. WSFC provides infrastructure features that support high-availability and disaster recovery scenarios for hosted server applications. If a cluster node or service fails, the services that were hosted on that node can be automatically or manually transferred to another available node in a process known as failover.
The nodes in a WSFC cluster work together to collectively provide the following types of capabilities:
- Distributed metadata and notifications
WSFC service and hosted application metadata is maintained on each node in the cluster. This metadata includes WSFC configuration and status in addition to hosted application settings. Changes to a node's metadata or status are automatically propagated to the other nodes in the cluster.
- Resource management
Individual nodes in the cluster may provide physical resources such as direct-attached storage, network interfaces, and access to shared disk storage. Hosted applications register themselves as cluster resources, and may configure startup and health dependencies upon other resources.
- Health monitoring
Inter-node and primary node health detection is accomplished through a combination of heartbeat-style network communication and resource monitoring. The overall health of the cluster is determined by the votes of a quorum of nodes in the cluster.
- Failover coordination
Each resource is configured to be hosted on a primary node, and each can be manually or automatically transferred to one or more secondary nodes. A health-based failover policy controls automatic transfer of resource ownership between nodes. Nodes and hosted applications are notified when failover occurs so that they can react appropriately.
Term |
Description |
|---|---|
Node |
A Microsoft Server system that is an active or inactive member of a server cluster. |
Cluster resource |
A physical or logical entity that can be owned by a node, brought online and taken offline, moved between nodes, and managed as a cluster object. A cluster resource can be owned by only a single node at any point in time. |
Resource group |
A collection of cluster resources managed as a single cluster object. Typically a resource group contains all of the cluster resources that are required to run a specific application or service. Failover and failback always act on resource groups. |
Resource dependency |
A resource on which another resource depends. If resource A depends on resource B, then B is a dependency of A. |
Network name resource |
A logical server name that is managed as a cluster resource. A network name resource must be used with an IP address resource. |
Preferred owner |
A node on which a resource group prefers to run. Each resource group is associated with a list of preferred owners sorted in order of preference. During automatic failover, the resource group is moved to the next preferred node in the preferred owner list. |
Possible owner |
A secondary node on which a resource can run. Each resource group is associated with a list of possible owners. Resource groups can fail over only to nodes that are listed as possible owners. |
Quorum mode |
The quorum configuration in a failover cluster that determines the number of node failures that the cluster can sustain. |
Forced quorum |
The process to start the cluster even through only a minority of the elements that are required for quorum are in communication. |