computer science

Redundant Array of Inexpensive Servers

Redundant Array of Inexpensive Servers is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Redundant Array of Inexpensive Servers rather than just read about it. In short: A Redundant Array of Inexpensive Servers (RAIS) or Redundant Array of Independent Nodes (RAIN) is the use of multiple servers to maintain service if one server fails. This is similar in concept to how RAID turns a cluster of ordinary disks into a single block device.

Key takeaways

Redundant Array of Inexpensive Servers belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Redundant Array of Inexpensive Servers to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Redundant Array of Inexpensive Servers from memory before moving on to harder problems.

Reference excerpt

A Redundant Array of Inexpensive Servers (RAIS) or Redundant Array of Independent Nodes (RAIN) is the use of multiple servers to maintain service if one server fails. This is similar in concept to how RAID turns a cluster of ordinary disks into a single block device. RAIS was designed to provide the benefits of a symmetric multiprocessor system (SMP) at the entry cost of computer clusters. The term may imply some kind of load balancing between the servers.

Technology RAIS is a simple, high performance, mainframe-grade alternative to more expensive enterprise computing infrastructure solutions. It turns an array of ordinary servers into a single virtual machine, similar in concept to how RAID turns a cluster of ordinary disks into a single block device. Every RAIS node is a stateless computing unit. RAIS stripes and mirrors application code and memory across an array of ordinary servers using the standard RAID schemata of level 0, level 1, level 5, level 1+0. This is possible through a memory management system called Versioned Memory. Data blocks of each stream are striped across the array servers. A fast packet switch is used to connect server and client stations. Each server has a dedicated network segment, and each client contacts the server one by one. Each server has its own storage, CPU, and network segment. The server capacity increases with the number of servers. In a manner more usually associated with high cost SMP architectures, RAIS achieves this by turning a cluster of independent servers into a single large server running applications across a virtualised network of nodes. The concept is similar to how RAID stripes and mirrors data across multiple independent disks and code of an application program across multiple independent nodes of a cluster. The applications see only a single logical shared memory which functions as a binary compatible SMP system. If the data is split into segments and distributed between multiple storage providers, the technology has applications for improving confidentiality in cloud computing.

See also Disk array controller Disk Data Format (DDF) Vinum volume manager

References

Worked examples

Example 1 — a first encounter with Redundant Array of Inexpensive Servers

Start with the simplest possible case. Write down what Redundant Array of Inexpensive Servers claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Redundant Array of Inexpensive Servers before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Redundant Array of Inexpensive Servers ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Redundant Array of Inexpensive Servers

In research: Redundant Array of Inexpensive Servers appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Redundant Array of Inexpensive Servers in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Redundant Array of Inexpensive Servers is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computing stubs, Servers (computing), so understanding it makes those chapters shorter.
In everyday life: Look for Redundant Array of Inexpensive Servers outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Redundant Array of Inexpensive Servers in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Redundant Array of Inexpensive Servers means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Redundant Array of Inexpensive Servers out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Redundant Array of Inexpensive Servers in simple terms?

Why does Redundant Array of Inexpensive Servers matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Redundant Array of Inexpensive Servers?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Redundant Array of Inexpensive Servers.