computer science

Highly Available STorage

Highly Available STorage 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 Highly Available STorage rather than just read about it. In short: Highly Available Storage (HAST) is a protocol and tool set for FreeBSD written by Pawel Jakub Dawidek, a core FreeBSD developer. HAST provides a block device to be synchronized between two servers for use as a file system.

Key takeaways

Highly Available STorage 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 Highly Available STorage to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Highly Available STorage from memory before moving on to harder problems.

Reference excerpt

Highly Available Storage (HAST) is a protocol and tool set for FreeBSD written by Pawel Jakub Dawidek, a core FreeBSD developer. HAST provides a block device to be synchronized between two servers for use as a file system. The two machines comprise a cluster, where each machine is a cluster node. HAST uses a Primary-Secondary (or Master-Slave) configuration, so only one cluster node is active at a time. HAST-provided devices appear like disk devices in the /dev/hast/ directory in FreeBSD, and can be used like standard block devices. HAST is similar to a RAID1 (mirror) where each RAID component is provided across the network by one cluster node.

See also Network block device DRBD (Distributed Replicated Block Device)

References

External links HAST page at FreeBSD wiki HAST at FreeBSD HandBook

Worked examples

Example 1 — a first encounter with Highly Available STorage

Start with the simplest possible case. Write down what Highly Available STorage 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 Highly Available STorage 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 Highly Available STorage 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 Highly Available STorage

In research: Highly Available STorage 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 Highly Available STorage 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: Highly Available STorage is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications protocols, Computing stubs, FreeBSD, so understanding it makes those chapters shorter.
In everyday life: Look for Highly Available STorage 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 Highly Available STorage in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Highly Available STorage 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 Highly Available STorage out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Highly Available STorage in simple terms?

Why does Highly Available STorage 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 Highly Available STorage?

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 Highly Available STorage.