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{{Short description|Set of computers configured in a distributed computing system}}
{{Distinguish|data cluster|grid computing}}
{{Redirect|Cluster computing|the journal|Cluster Computing (journal)}}
[[File:MEGWARE.CLIC.jpg|thumb|Technicians working on a large [[Linux]] cluster at the [[Chemnitz University of Technology]], Germany]]
[[File:Sun Microsystems Solaris computer cluster.jpg|thumb|Sun Microsystems [[Solaris Cluster]], with [[Close Coupled Cooling#In-Row Air Conditioners|In-Row cooling]]]]
[[File:Taiwania series.jpg|thumb|[[Taiwania_(supercomputer)|Taiwania]] series uses cluster architecture
A '''computer cluster''' is a set of [[
The components of a cluster are usually connected to each other through fast [[local area network]]s, with each [[Node (networking)|node]] (computer used as a server) running its own instance of an [[operating system]]. In most circumstances, all of the nodes use the same hardware<ref>{{cite web |url=https://stackoverflow.com/questions/9723040/what-is-the-difference-between-cloud-grid-and-cluster |title=Cluster vs grid computing |website=[[Stack Overflow]]}}</ref>{{better source needed|date=June 2017}} and the same operating system, although in some setups (e.g. using [[Open Source Cluster Application Resources]] (OSCAR)), different operating systems can be used on each computer, or different hardware.<ref name=pcauthority>{{cite web|url=http://www.pcauthority.com.au/Feature/306972,weekend-project-build-your-own-supercomputer.aspx|title=Weekend Project: Build your own supercomputer|date=29 June 2012|first=Darien|last=Graham-Smith|website=PC & Tech Authority|access-date=2 June 2017}}</ref>
Clusters are usually deployed to improve performance and availability over that of a single computer, while typically being much more cost-effective than single computers of comparable speed or availability.<ref>{{cite web|url=http://www.cc.gatech.edu/~bader/papers/ijhpca.html|title=Cluster Computing: Applications|last1=Bader|first1=David|author-link=David Bader (computer scientist)|date=May 2001|publisher=[[Georgia Institute of Technology College of Computing|Georgia Tech College of Computing]]|first2=Robert|last2=Pennington|access-date=2017-02-28|archive-url=https://web.archive.org/web/20071221011621/http://www.cc.gatech.edu/~bader/papers/ijhpca.html|archive-date=2007-12-21|url-status=dead}}</ref>
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"[[Load balancing (computing)|Load-balancing]]" clusters are configurations in which cluster-nodes share computational workload to provide better overall performance. For example, a web server cluster may assign different queries to different nodes, so the overall response time will be optimized.<ref name=Sloan>{{cite book|title=High Performance Linux Clusters|url=https://archive.org/details/highperformancel0000sloa|url-access=registration|first=Joseph D.|last=Sloan|year=2004|publisher="O'Reilly Media, Inc." |isbn=978-0-596-00570-2}}</ref> However, approaches to load-balancing may significantly differ among applications, e.g. a high-performance cluster used for scientific computations would balance load with different algorithms from a web-server cluster which may just use a simple [[round-robin scheduling|round-robin method]] by assigning each new request to a different node.<ref name=Sloan />
Computer clusters are used for computation-intensive purposes, rather than handling [[Input/output|IO-oriented]] operations such as web service or databases.<ref name=VECPAR >{{cite book|title=High Performance Computing for Computational Science – VECPAR 2004|first1=Michel|last1=Daydé|first2=Jack|last2=Dongarra|year=2005|isbn=978-3-540-25424-9|pages=120–121|publisher=Springer }}</ref> For instance, a computer cluster might support [[Computer simulation|computational simulations]] of vehicle crashes or weather. Very tightly coupled computer clusters are designed for work that may approach "[[supercomputing]]".
"[[High-availability cluster]]s" (also known as [[failover]] clusters, or HA clusters) improve the availability of the cluster approach. They operate by having redundant [[Node (networking)|nodes]], which are then used to provide service when system components fail. HA cluster implementations attempt to use redundancy of cluster components to eliminate [[single point of failure|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.
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==Benefits==
<!-- This used to be a list. Work has been done since, but it's still incomplete. -->
Clusters are primarily designed with performance in mind, but installations are based on many other factors. Fault tolerance (''the ability
In terms of scalability, clusters provide this in their ability to add nodes horizontally. This means that more computers may be added to the cluster, to improve its performance, redundancy and fault tolerance. This can be an inexpensive solution for a higher performing cluster compared to scaling up a single node in the cluster. This property of computer clusters can allow for larger computational loads to be executed by a larger number of lower performing computers.
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===Data sharing===
[[File:Nec-cluster.jpg|thumb|A [[NEC]] [[Nehalem (microarchitecture)|Nehalem cluster]]]]
As the computer clusters were appearing during the 1980s, so were [[supercomputer]]s. One of the elements that distinguished the three classes at that time was that the early supercomputers relied on [[Shared memory architecture|shared memory]].
However, the use of a [[clustered file system]] is essential in modern computer clusters.{{Citation needed|date=August 2013}} Examples include the [[IBM General Parallel File System]], Microsoft's [[Cluster Shared Volumes]] or the [[Oracle Cluster File System]].
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==Cluster management==
[[File:Cubieboard HADOOP cluster.JPG|thumb|Low-cost and low energy tiny-cluster of [[Cubieboard]]s, using [[Apache Hadoop]] on [[Lubuntu]]]]
[[File:Circumference C25 (41227579055).png|thumb|A pre-release sample of the Ground Electronics/AB Open Circumference C25 cluster [[
One of the challenges in the use of a computer cluster is the cost of administrating it which can at times be as high as the cost of administrating N independent machines, if the cluster has N nodes.<ref name=patter641 >{{cite book|title=Computer Organization and Design|first1=David A.|last1=Patterson|first2=John L.|last2=Hennessy|year=2011|isbn=978-0-12-374750-1|pages=641–642|publisher=Elsevier }}</ref> In some cases this provides an advantage to [[shared memory architecture]]s with lower administration costs.<ref name=patter641 /> This has also made [[virtual machine]]s popular, due to the ease of administration.<ref name=patter641 />
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:* [[Solaris Cluster]]
:* [[Veritas Cluster Server]]
:* [[Beowulf cluster]]
''Computer farms''
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{{Commons category|Clusters (computing)}}
* [https://web.archive.org/web/20190219183441/https://www.ieeetcsc.org/ IEEE Technical Committee on Scalable Computing (TCSC)]
* [https://archive.today/20130103192843/http://publib.boulder.ibm.com/infocenter/clresctr/vxrx/index.jsp?topic=
* [https://www.ibm.com/developerworks/wikis/display/tivoli/Tivoli+System+Automation Tivoli System Automation Wiki]
* [https://static.googleusercontent.com/media/research.google.com/en/us/pubs/archive/43438.pdf Large-scale cluster management at Google with Borg], April 2015, by Abhishek Verma, Luis Pedrosa, Madhukar Korupolu, David Oppenheimer, Eric Tune and John Wilkes
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