Terms and Definitions
Quorum Resource: A dedicated drive that both cluster servers share to store and retrieve quorum information.
This resource creates and logs data that is critical to recovery when servers fail to communicate with each other. This data can be owned by one cluster server at a time only and is used to determine which server will take ownership of the resources if the two servers cannot communicate with each other.
When the quorum owner fails, the surviving server takes over ownership of that quorum drive and all the other resources in the cluster.
This drive is a critical component of the cluster.
If the quorum drive becomes defective, recovery is impossible.
A quorum drive must be configured as RAID level 1.
Failback: This is a special case of failover and is the process of moving back some or all groups of resources to the preferred owner after a failover has occurred.
The preferred owner is the server in the cluster on which you prefer each group of resources to run.
If the preferred owner fails, its resources are transferred to the other server.
When the preferred owner is repaired and comes back online, and allow failback is enabled in the Microsoft Cluster Administration Program, the resources are automatically transferred back to that server.
Failover: This is the process of relocating the cluster resources from a failed server to the surviving server.
The detection of a failure is made by the resource-monitor program responsible for the resource.
If a resource failure occurs, the resource-monitor program notifies the Cluster Service, which triggers the actions defined in the failover policy for that resource.
A failover can occur automatically, such as when an application or a server fails, or it can occur manually, such as when a system administrator moves all applications onto one server and then brings the other server down for scheduled maintenance.
Failover generally consists of three parts:
Resource Group: Dependent resources that are grouped together.
Some resources need other resources to run successfully and are known as resource dependencies .
When one resource is listed as a dependency for another resource, the two resources must be placed in the same group.
If all resources are ultimately dependent on one resource (for example, one physical disk resource), all resources must be in the same group.
It is possible that all resources in a cluster will need to be in one group.
Also, any cluster operation performed on a group is performed on all resources that are present within that group.
For example, if a resource needs to be moved from Server A to Server B, all the resources defined in the group that the resource is in will be moved.
SCSI Heartbeat Connection: This is a small computer system interface (SCSI) cable connection that joins two IBM ServeRAID II adapters, one in each server, together.
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