Home > Articles

This chapter is from the book

Computation Clusters

Linux clustering capabilities using Beowulf have previously been mentioned and the advantages have been outlined. This section covers in more detail what clustering can be used for, how it works, and how it can be configured. Clustering for high availability as well as high-performance computing is providing companies, large and small, peace of mind and solidly reliable IT services, as well as supercomputing capabilities for a fraction of the traditional cost.

Linux clustering can be useful to meet both high availability and high-performance needs. Examples of high availability include web and e-commerce geo-site redundancies, high-demand application failover contingencies, distributed applications, and load balancing. High-performance cluster candidates include finite element analysis, bioscience modeling, animation rendering, seismic analysis, and weather prediction.

High-Availability Clusters

IDC estimated that 25% of all high-performance computing shipments in 2003 were clusters. It's an area that is growing at a considerable rate. Organizations that are using clustering to create high-performance solutions include Google (10,000 node cluster), Overstock.com (Oracle database for product tracking), Burlington Coat Factory (IBM PolyServe clustering), Epiphany, and many more.

Here's how high availability clusters work—starting with a simple two-node cluster and building from there. Assume that the services you want to ensure are "always available" are email, NFS, and a web server. For a two-node cluster, you will have at least two servers—each with a storage drive and identical copies of each of the services installed (mail, NFS, web). These servers are connected together with two to three connections. The first connection is a dedicated serial cable that supports the Heartbeat service, which constantly monitors the status of each service (mail, NFS, web). If Heartbeat detects that one or more of the services has failed, it immediately starts the same service(s) on the second server.

The second connection between the two clustered servers is a dedicated data connection for keeping drives on both systems mirrored and in sync. 100MB or gigabyte connections are recommended here, especially if your services are data intensive and often changing. If a service suddenly switches to the second machine, the data that it may require will be there and ready. This high-speed data connection could also service the Heartbeat. Assuming these services (mail, NFS, web) are for web clients, there will be a third connection that links the servers to the network or the Internet. To play it safe, you should have an uninterruptible power supply (UPS) for each server that will be attached via UPS control cables.

Heartbeat and the application that keeps data storage in sync, DRDB, are both available with SUSE Linux and can be installed and managed through YaST. They are also available with other Linux distributions or from popular Linux sites. You have the options of configuring failover to occur immediately upon fault detection, initiating a manual failover, or specifying that failover operations occur in a specific order according to rules based on resource priority or system availability (see Figure 3.12).

Figure 3.12Figure 3.12 Simple two-node cluster for high-availability failover.

Now that you understand cluster basics, you can mix and match, adding servers and services to create any configuration that meets your needs. High-availability clusters can range from simple to very complex. You don't have to mirror the exact services on each machine. You can specify that one service on machine A fails over to machine B, and another service on machine A fails over to machine C. If you don't want the expense of duplicate hardware for every set of services, you could configure one machine to be the failover recipient for several other machines. The chances are slim that two or three machines would fail at once, overloading the target server. You could also have active services running on several servers (no idle failover machines) with failover to other servers in the cluster running other services.

Clustering provides a lot of flexibility for storage configuration. Instead of failing from drives on one machine to drives on another, you could create a storage array with combinations of RAID, mirroring or striping. These storage subsystems could also be configured to fail over to other systems, if that level of redundancy is needed. The possibilities are endless, and with the Internet and technologies such as iSCSI, a cluster can be geographically distributed.

If you've ever wondered what an extra "9" of availability gives you, here's a summary chart of how often you would be down in one year given a specific level of reliability. With high availability clusters on Linux, it's easy to reach five 9s.

  • 1   90.0000%   37 days

  • 2   99.0000%   3.7 days

  • 3   99.9000%   8.8 hours

  • 4   99.9900%   53 minutes

  • 5   99.9990%   5.3 minutes

  • 6   99.9999%   32 seconds

High-Performance Cluster

When it comes to high-performance computing on Linux, each high-performance cluster consists of one master and as many slave nodes as needed. Some of today's largest clusters have over 10,000 nodes. All nodes should be the same architecture (Intel, Apple, and so on) and for optimal performance, the hardware configurations should be identical (a slow node can slow down the entire cluster). Because the master node performs management functions, more RAM and faster network, processor, and disk speeds are highly recommended for better performance.

Linux is installed on every node and the application to be run on the cluster is installed on the master. Applications generally must be parallelized (written to take advantage of multiple processors) before computation can be spread across multiple computers for high-performance results. The exception is a serial application that is run repeatedly on different data sets.

The clustering software, which could be Beowulf or any other open source or commercial version, is also installed on the master node and every node in the cluster. The clustering software for high performance includes message-passing libraries that facilitate high-speed communication between nodes. Effective high-performance clusters also require high-speed connections between nodes. This can be provided using several methods, such as Ethernet, Gigabit Ethernet, or one of the commercial high-bandwidth, low-latency interconnect systems from vendors such as Myrinet, Infiniband, or Quadrics (see Figure 3.13).

Figure 3.13Figure 3.13 High-performance clusters consist of a master, slave nodes, and a high-speed switch.

With Linux, both high-availability and high-performance clusters can be created without added expense. The Heartbeat and Beowulf solutions are open source, and are included with the Novell SUSE Linux distribution. Novell gives you clustering right out of the box for either SUSE Linux or NetWare with basic versions of Open Enterprise Server. A Novell advantage is that Linux nodes can fail over to NetWare nodes and vice versa. A two-node cluster license is included that allows you to create mirrored or failover systems to ensure that data or applications are always available.

A major advantage to Linux clusters is that they are incrementally scalable. It doesn't take a complete redesign of an application or buying a new supercomputer to get more horsepower. You just augment the cluster by one, two, five, or 50 machines or more, depending on what you need to get the job done.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020