What is a Server Cluster?
Server Cluster is a group of independent servers which are called as nodes, works together as a single system and provides services to the clients with great availability. A cluster consists of two or more computers which work together with high reliability, scalability, and availability than a single computer. When there is a failure in one node in a cluster, then the resources will be directed and the workload can be distributed to another computer in the cluster. It ensures that the users can have constant access to the resources.
Server Clusters are designed for the applications with longer running memory state or for frequently updated data. It can be used in file servers, print servers, database servers, and messaging servers. It can maintain the consistency of the server even when there is any failure in one of the servers. The common devices to the server such as disks in common disk arrays and the connection media for accessing the disks are managed by only one server at a time.
Types of Server Clusters:
Based on the connection of nodes, the devices can store the cluster configuration and data. The data is stored in a resource called quorum resource and this quorum resource contains the data about a set of cluster configuration information and records of changes in the configuration. The three types of Server Clusters are
- Single quorum device cluster or standard quorum cluster
- Local quorum cluster or single node cluster
- Majority node set cluster
Single Quorum Device Cluster:
This is mostly used cluster type which is also known as standard quorum cluster. In this type, multiple nodes are connected to one or more cluster disk arrays. Each disk array is managed by only one server at a time and it contains the quorum resource. These cluster disk arrays are also called as cluster storage. In this model, only one copy of the quorum data is maintained and stored in the shared storage device. All nodes in the cluster can access the quorum data but the quorum disk resource runs only on one node at a time.
Local Quorum Cluster:
Local Quorum Cluster is often used for the development of cluster application and testing purpose. It is also called as single node cluster and it can use the local quorum resource which is stored on a local hard disk storage. The main disadvantage of this model is that there is only one node so that if there is any failure, the whole group will become unavailable.
Majority Node Set Cluster:
Each node in the majority node cluster maintains an own copy of cluster configuration data. The configuration data will be consistent across the nodes. Since each node maintains a local copy of the quorum, the shared storage device is not necessary. So, this type of cluster can be deployed in a geographically distributed environment.