This is the presentation on clusters computing which includes information from other sources too including my own research and edition. I hope this will help everyone who required to know on this topic.
17. Clustering Methods CLUSTERING METHOD DESCRIPTION BENEFITS LIMITATIONS Passive standby A secondary server takes over in case of primary server failure Easy to implement High cost because the secondary server is unavailable for other processing tasks Active standby The secondary server is also used for processing tasks Reduced cost because secondary servers can be used for processing Increased complexity Separate servers Separate servers have their own disks. Data are continuously copied from primary to secondary server High availability High network and server overhead due to copying operations Servers connected to disks Servers are cabled to the same disks, but each server owns its disk. If one server fails, its disks are taken over by the other server Reduced network and server overhead due to elimination of copying operations Usually requires disk mirroring or RAID technology to compensate for risk of disk failure Servers share disks Multiple servers simultaneously share access to the disks Low network and server overhead. Reduced risk of downtime caused by disk failure Requires lock manager software. Usually used with disk mirroring or RAID technology
Clusters are deployed to improve performance and/or availability over that of a single computer, while typically being much more cost-effective than single computers of comparable speed or availability.
High-availability clusters (also known as Failover Clusters) are implemented primarily for the purpose of improving the availability of services that the cluster provides. They operate by having redundant nodes, which are then used to provide service when system components fail. The most common size for an HA cluster is two nodes, which is the minimum requirement to provide redundancy. HA cluster implementations attempt to use redundancy of cluster components to eliminate single points of failure. There are commercial implementations of High-Availability clusters for many operating systems. The Linux-HA project is one commonly used free software HA package for the Linux operating system.
Load-balancing is when multiple computers are linked together to share computational workload or function as a single virtual computer. Logically, from the user side, they are multiple machines, but function as a single virtual machine. Requests initiated from the user are managed by, and distributed among, all the standalone computers to form a cluster. This results in balanced computational work among different machines, improving the performance of the cluster system.
The cluster initially consisted of Power Mac G5s; the rack-mountable XServes are denser than desktop Macs, reducing the aggregate size of the cluster.
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