← QCE Digital Solutions Unit 2

Data security: availability

Authorised users can reach data and systems when they need them. Hardware failure and attacks can threaten it, so backups and protection keep a system running.

Part of: QCE Digital Solutions Unit 2 — Data and Programming Techniques — Module 49

Understanding Data security: availability in QCE Digital Solutions Unit 2

What it does: Mirroring copies data to a second disk. If one disk fails, the system keeps running, so the data stays available. Restoring from a backup brings data and systems back, so authorised users can reach them again after a failure or attack. Availability is about access when needed. Keeping data private is confidentiality, not availability. Firewalls filter harmful traffic. Deleting backups would make recovery harder and reduce availability. Availability is the part of data security that makes sure the right people can get to the data and system whenever they need to. The fix is to keep the firewall and other protection on. Availability depends on blocking attacks so authorised users can still get in.

Common mistakes: The condition needs the comparison operator = to check whether the disk has failed. <- assigns a value and does not compare. It should be: if disk = "failed" then. attempts starts at 0, so attempts > 5 is false straight away and the lockout loop never runs. An attack could keep guessing passwords. It should be: while attempts < 5.

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This module's key terms are also in a printable crossword (Modules 186–228) and word search (Modules 144–228).

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Learning

Duo

Which statement best describes availability in data security?

Authorised users can reach data and systems when they need themOnly one person is ever allowed to see the data

Matches

Only one server, no backup. If it fails, the school can just wait.

↓

A single point of failure threatens availability. One failed server stops all users, and with no backup the data may be lost.

Applying

Meanings

Term

Availability

Meaning

Authorised users can reach data and systems when they need them. Hardware failure and attacks can threaten it, so backups and protection keep a system running.

Practice

diskFailed <- true

Testing

Gaps

if serverStatus = "down"

Check Answer

Spots

1if disk <- "failed" then

2 server <- "backup"

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Quick Questions

1. Which statement best describes availability in data security?

A. Authorised users can reach data and systems when they need them ✓

B. Only one person is ever allowed to see the data

Availability is about access when needed. Keeping data private is confidentiality, not availability.

2. A school server's hard drive fails during exams and students cannot open their files. Which part of security is affected?

A. Confidentiality

B. Availability ✓

The data is not leaked, but users cannot reach it. That is a loss of availability caused by hardware failure.

3. Which action helps protect availability if a hardware failure happens?

A. Keeping regular backups and a spare system ✓

B. Using a longer username

Backups and spare hardware let a system be restored or keep running when a part fails.

4. A DoS attack floods a website with so many requests that real users cannot log in. What does it threaten?

A. Availability ✓

B. Data entry validation

A denial-of-service attack overloads a system so authorised users cannot reach it.

5. True or false: A system that is switched off by a power failure has lost availability.

A. False

B. True ✓

If authorised users cannot reach the system when they need it, availability is lost, even if no one attacked it.

Match the Pairs

Availability → Authorised users can reach data and systems when they need them

DDoS attack → An attack that floods a server with traffic so real users cannot reach it

A hardware failure such as a dead disk can make data unavailable, so a copy is kept on a second drive → RAID 1 mirror: disk A and disk B hold the same data

A backup stored off-site lets a school restore data after a failure or an attack and get users working again → restore(backup_2026_03_01)

Only one server, no backup. If it fails, the school can just wait. → A single point of failure threatens availability. One failed server stops all users, and with no backup the data may be lost.

Firewall switched off to make the website faster. → Turning off the firewall leaves the system open to attacks such as DDoS, which can knock the website offline for authorised users.

Key Term

Availability

Authorised users can reach data and systems when they need them. Hardware failure and attacks can threaten it, so backups and protection keep a system running.

Fill in the Blanks

1. if serverStatus = "down" then print("Switch to backup server") end if

Hint: Type the keyword that follows the condition in an if block.

2. if requestsPerMin > limit then block(ipAddress) end if

Hint: Type the comparison operator that checks whether the attack traffic is above the limit.

3. if diskFailed = true then restore(backup) end if

Hint: Type the function name that recovers data from the backup copy after a hardware failure.

4. while serverUp = false do reconnect(server) end while

Hint: Type the loop keyword that keeps repeating while the condition holds.

5. hoursUp <- 98 totalHours <- 100 uptime <- hoursUp / totalHours * 100

Hint: Type the arithmetic operator that divides the hours up by the total hours to help work out an availability percentage.

Spot the Error

Question 1

A if disk <- "failed" then

B server <- "backup"

C else

D server <- "main"

E end if

Line A — The condition needs the comparison operator = to check whether the disk has failed. <- assigns a value and does not compare. It should be: if disk = "failed" then.

Question 2

A attempts <- 0

B while attempts > 5

C input password

D attempts <- attempts + 1

E print "Account locked"

Line B — attempts starts at 0, so attempts > 5 is false straight away and the lockout loop never runs. An attack could keep guessing passwords. It should be: while attempts < 5.

Question 3

A files <- 120

B backedUp <- 0

C for i from 0 to files

D backedUp <- backedUp + 1

E print backedUp

Line C — Starting at 0 makes the loop run 121 times, so it counts one more backup than there are files. The backup count would be wrong. It should be: for i from 1 to files.

Question 4

A serverUp <- false

B if serverUp = true then

C print "Use backup server"

D end if

Line B — The backup server should be used when the main server is down, so the test must be serverUp = false. As written, it switches to the backup while the main server is working.

Question 5

A lastBackup <- 9

B limit <- 7

C if lastBackup > limit then

D print Backup is overdue

E end if

Line D — The text to display must be in quotation marks. Without them, Backup is overdue is treated as code and not as a string. It should be: print "Backup is overdue".

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