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Definition And Characteristics Of Cluster Computing

The advancement of sites and especially the Internet is the fact that nowadays, they need more resources to process data more quickly. Given that the use of any machine could not meet these requirements, it appeared that the work of distributing the areas over several machines to run simultaneously would cure this problem.

In here are some, we describe the various characteristics of any cluster and its own various categories. Then we will look networks (architecture, topologies, components, . . . ). Then finally we will discuss how communications are in clusters.

2 Description and characteristics of the cluster

We're talking about clustering, server cluster or farm Computing Solutions for artist consolidate multiple unbiased computers (called nodes) to enable management

comprehensive and go beyond the limitations of the computer to:

- Increase availability

Facilitating the scalability

- Enable load balancing

- Facilitate management of resources (CPU, Ram memory, devices, network bandwidth).

Clusters of servers are an inexpensive method, residing in the establishment of multiple computers

apparatre network that will be an individual computer with more capabilities (more powerful, etc. . ), these are widely used for parallel processing. This maximizes use of resources permits the circulation of different treatments on nodes. A major good thing about a cluster is he no longer need to buy expensive multiprocessor servers but it is currently possible to settle for smaller systems that can connect to the next someone to other according to changing needs. There will vary types of cluster:

- Expanded distance cluster: This is a cluster with nodes located in various data centers separated by distance. Prolonged distance clusters are linked through a cable which guarantees high-speed network access between nodes until all the rules for the mistake tolerant architecture are followed. The maximum distance between nodes in a cluster distance scope is defined by the limitations of technology and data replication boundaries networking.

- Metropolitan Cluster: This cluster geographically distributed within the confines of a metropolitan area demanding authorization for processing of cabling and network components for data replication redundant.

- Continental Cluster: That is a group of clusters that use systems of streets and service sites general population data replication and cluster communication to support failover deal between different clusters in several data centers. Continental clusters tend to be located in different towns or countries and may expand over hundreds or thousands of kilometer.

3 General structures of your cluster

A cluster is essentialy constructed by several machine (PC, server. . . ), operating-system, interconexion systems, parallel programming environment, middleware and application-


Fig 1 : General architecture of any cluster

4 Differents classes of Cluster

4. 1 High availibility cluster

4. 1. 1 Architecture

Fig 2 : Structures of an hight availibility cluster

4. 1. 2 Definition

High supply clusters are being used to protect one or more sensitive applications. To get this done, the application and all the resources necessary for it'll be controlled permanently. For powerful safety software, include this security in the hardware, the network and operating system. Generally, several products are used to protect multiple applications on the same node but there are solutions that can protect as many applications as you want. With these alternatives, we aren't obliged to improve all applications and can be produced case by circumstance basis.

If the cluster software reconnat failing then, initially, it'll make an effort to restart the X source of information both locally on the same node.

Then, if this source does not restart, the program will start the application form switch to another node. Regardless, the client will observe that the application is situated on another node in the cluster and their gain access to Request as before. The normal high supply clusters contain only a few nodes but may use clusters involving 32 or 64 knots. In case a cluster contains more than two nodes, so we can identify different transitioning planes. This is useful to decrease the reduced amount of performance after a seesaw.

4. 2 High Performance cluster

4. 2. 1 Architecture

Fig 3 : Structures of your hight performance cluster

4. 2. 2 Definition

The main function of a higher performance cluster (also called High Performance Technical Clustering HPC) is to increase the ability of a Computer. To execute this, it's important to cut the stain that is carried out into sub-tasks. The result is the total sub-tasks. The Management Device - to organize all the sub duties - and the node that will get the result are the only critical items (solo point of failing). These components can be protected with a high availableness cluster. The crash of 1 of the nodes is not really a disaster because the work of this node can be carried out by another. The performance of the cluster but it'll weaken the cluster

always work.

4. 3 Load balancing cluster


Fig 4 : Structures of lots balancing cluster


A Cluster is lots balancing server farm with the same function. A splitter is required to distribute the demands of users each node, it verifies that every node gets the same workload. The application form will be delivered to the node that has the fastest amount of time in respond to it. This algorithm provides better performance at anytime. The performance of the cluster rely upon the dispatcher. It will choose the node that gets the opportunity to addresses the use of the user as quickly as possible. Without any safety the cluster load balancing can be a SPOF (solitary point of inability). Best is to add redundancy to the cluster. If one node is no more in working condition, the cluster will continue to work as same. The dispatcher will identify the dead node and will include more in its calculations, the entire performance of the cluster then it will reduce. The web-server farms (Yahoo. . . ) represent an example of cluster fill balancing.

5 Inteconnexion technologies

Today, advanced network solutions help achieve more efficient cluster. These must combine the acceleration interconnect technologies to aid the extensive bandwidth and low latency communication between nodes in the cluster. Because both of these indicators measure the performance of interconnects. The selection of a technology cluster interconnect network relies several factors, such as compatibility with the hardware in the cluster, the operating system, price and performance. In what follows, we will detail a few of the most used systems.

5. 1 Myrinet

Myrinet (ANSI / VITA 26-1998) is a high-speed network protocol created by Myricom to be utilized as system interconnect multiple machines developing a cluster. Myrinet causes much less over head network alone communication protocol that most used protocols such as Ethernet, and then offers an increased bandwidth, less interference and less latency with all the system processor. Though it can be used as a normal network standard protocol, Myrinet is often utilized by programs that learn how to use it straight, negating the necessity for system telephone calls. Physically, Myrinet uses two dietary fiber optic cables, one for sending data and one for reception, each linked to a machine with a single connector. The machines in question are linked to one another through routers and switches with low latency (the machines aren't directly connected to each other). Myrinet also offers some features that improve tolerance to problems, mostly monitored by the switches. These features include circulation control, problem control and status monitoring of each physical connection. The fourth and last version of Myrinet, also named Myri-10G facilitates a throughput of 10 Gbps which is interoperable in terms of physics with 10 Gbps Ethernet standard (cords, connectors, distance, kind of indication).

5. 2 Infiniband

It is a computer bus has high-speed. It is intended to both interior and external marketing communications. It is the consequence of the merger of two rivalling technologies, Future I / O, developed by Compaq, IBM, and Hewlett-Packard, with Next Generation I / O (ngio), developed by Intel, Microsoft, and Sun Microsystems. InfiniBand runs on the bi-directional bus with low priced, and enjoying a low latency. But he'll remain very fast, as it offers a throughput of 10 Gbps in each path. InfiniBand runs on the technology which allows multiple devices to concurrently gain access to the network. Data are transmitted as packets, which collectively form text messages. The InfiniBand is now widely used in the world of HPC (POWERFUL Computing) as a PCI-X or PCI-Express APPOINTED HCA (Variety Channel Adapter) functioning at 10 Gbit / s (SDR, One Data Rate), 20 Gbps (DDR, Double Data Rate) or 40 Gbit / s (QDR Quad Data Rate). It also requires specialized network using switches (or switches) and InfiniBand copper wires or type CX4

Fiber for long distances (using an adapter to Dietary fiber CX4). The protocol allows the use of InfiniBand

these cards natively by using the protocol VERBS or software overlays:

- IPoIB (IP over InfiniBand) that displays an Ethernet part together with Infiniband and so the probability to configure an IP over InfiniBand slots.

- SDP (Sockets Direct Protocol), which presents a socket part over InfiniBand.

- SRP (SCSI RDMA Protocol) which allows frames to encapsulate SCSI over InfiniBand. Some manufacturers offer windows InfiniBand attached storage somewhat than Fibre Channel.

These overlays offer lower performance in the local protocol, but are much easier to use because they

not require the redevelopment of applications to use the InfiniBand network. In the world of HPC libraries MPI (Message Passing User interface) generally use the native layer to deliver directly VERBS

best possible performance.

Gigabit Ethernet

Gigabit Ethernet (GbE) is a term used to spell it out a number of systems used to implement the Ethernet standard has a data copy rate of 1 gigabit per second (or 1000 megabits per second). These systems derive from twisted match copper cable television or fiber optics. They can be described by the IEEE 802. 3z and 802. 3ab. Unlike other Ethernet technologies, Gigabit Ethernet provides flow control. The systems on which they can be found will be more reliable. They include FDR, or "Full-Duplex Repeaters that allow multiplex lines, using buffers and localized movement control to boost performance. The majority of its switches are constructed as new modules for different models of suitable Gigabit switches already can be found.

5. 4 SCI (Scalable Coherent Interface)

SCI Scalable Coherent Interface, IEEE Standard 1596-1992 is a providing a distributed storage system has low latency across a cluster. SCI may use a memory increasing to the group of the cluster, thus ridding the programmer to control this complex. This is regarded as a kind of BUS INPUT / Result processor-memory via a LAN. The facilities of coding it offers and the fact that SCI is an IEEE standard has managed to get a fairly popular choice for the interconnection of machines in a higher performance cluster.

6 Comparability of Interconnect technologies

This contrast includes the key standards for judging the performance of an cluster and by

needs and sources of each organization solutions will change.

Gigabit Ethernet





< 100



< 320

Latency (s)

< 100

< 7



Max nods


> 1000



Table 1 : Assessment of Interconnects technologies

7 Performing test

A group of authors Pourreza, Eskicioglu and Graham led the ratings performance of a number of technologies we have presented

above. The parameter they have taken into account is the timing of the execution of the same applications on cluster nodes equivalent. They tested lots of standard algorithms namely NAS Parallel Benchmark and the Pallas Benchmark plus some applications of parallel computing the real world on the first and second generation Myrinet, SCI, but also on FastEthernet (100Mbps) and Gigabit Ethernet (1000Mbps). The results obtained are presented below. These assessments were performed on a cluster has eight nodes under RedHat 9. 0 with kernel 3. 2. 2 and gcc 2. 4. 18smp. Each node has:

- A dual Pentium III;

- a 550 MHz processor with 512 MB of SDRAM storage area shared;

- local disks (all activities of entry-exit in the experiments are performed on local disks to get rid of the effects of access to NFS).

Each node also has the first and second years of Myrinet, Fast Ethernet, Gigabit Ethernet network software credit card and point-to-point SCI (Dolphin WulfKit). All interfaces of network credit cards are linked to dedicated switches except those of SCI which are connected to a mesh configuration (2x4).

7. 1 Bandwidth

Fig 6 : Bandwith of four interconnects H. Pourreza, Graham, Eskicioglu


Fig 7 : Latency of four interconnects H. Pourreza, Graham, Eskicioglu

The basic performance of different interconnect technologies in terms of bandwidth and latency are presented respectively in Statistics 1 and 2. This means that that Fast Ethernet is significantly less than all the others, and Gigabit Ethernet is visibly lower than SCI and Myrinet implies that despite a bandwidth considerably similar. From these results, it is clear that Fast Ethernet is most likely only well suited for applications related to the computation.


The competitive characteristics of business and progress of research domains have created a dependence on personal computers scalable, versatile and reliable. Advanced applications now require a sizable computing ability. Clusters give a solution to his problems. Clusters stand for a guaranteeing future for this new notion provides scalability in the world of data processing.

Thanks to the several systems we use to put into action them, there are sites that are becoming performants. Because these new systems can have high bandwidth and low latency. Performance assessments completed have showed that some systems were more efficient than others. When establishing the cluster, it should choose an architecture and an appropriate network topology to avoid excessively reducing network performance. The use of cluster is less costly than buying a supercomputer, since it uses the sources of several machines on which the areas are distributed and almost all of the clusters using the Linux operating-system which really is a powerful system around due to its versatility, workability and low cost.

Sources :

The essence of Distributed Systems : Joel M. Crichlow

Parallel Processing, Theory and Comparisons : G. Jack Lipovski, Miroslaw Malek

Parallel Personal computers : Hockney Jesshope

Parallel and Distributed Computation, Numerical Methods :Dimitri P. Bertsekas, John N. Tsitsilklis.

Practical Parallel Control, An launch to problem solvin in Parallel : Alan Chalmers and Jonathan Tidmus.

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