Summer 2023Q5(B) OR
Discuss RAID.
Chapter 5
RAID and Disk Cache
Understand RAID goals, level trade-offs, and cache-based disk performance improvements.
Estimated time: 20 min
RAID combines disks for speed and/or fault tolerance; disk cache keeps recently used sectors for faster access.
You often need to justify which RAID level fits a practical scenario.
RAID Trade-offs
From notesClear explanation
RAID levels differ in striping granularity, parity design, performance, rebuild cost, and fault tolerance.
What it really means
You trade usable space and write complexity for reliability and read speed.
Key takeaway
Always state both performance and reliability implications.
Disk Cache Role
From notesClear explanation
Disk cache stores recently or likely-needed sectors in faster memory, reducing average read latency.
What it really means
Like keeping frequently used books on your desk instead of shelf every time.
Key takeaway
Caching improves perceived speed without changing disk mechanics.
How RAID Levels Work
Added clarityClear explanation
RAID 0 stripes blocks across disks for speed without recovery, RAID 1 duplicates data on mirror disks, RAID 5 distributes parity blocks so data can be rebuilt after one-disk failure.
What it really means
Striping splits work, mirroring copies work, parity helps reconstruction.
Example
If one disk fails in RAID 5, missing block is recalculated using parity from surviving disks.
Key takeaway
Answer RAID questions by comparing speed, capacity, and fault tolerance together.
- - Calling RAID 0 fault tolerant
- - Ignoring write penalty in mirrored/parity schemes
- - Not distinguishing dedicated vs distributed parity
- - RAID 0: striping only, no redundancy
- - RAID 1: mirroring, high reliability but half usable capacity
- - RAID 5: distributed parity balancing performance and resilience
- - Disk cache reduces repeated access latency
RAID 1 usable capacity (two-disk mirror) = size of one disk
Exam lens for this topic
What evaluators usually expect in structured exam answers.
Must-use keywords
- - raid
- - striping
- - mirroring
- - parity
- - disk cache
Answer flow
- - Write exact definition in first line
- - Explain mechanism in ordered bullets
- - Add one short example or scenario
- - Close with key takeaway and one exam keyword
Practice Questions
Define RAID and explain RAID0, RAID1, RAID2.
Source: Summer 2024 Q5(A)
Answer focus: Core mechanism and trade-offs per level.
Discuss RAID.
Source: Summer 2023 Q5(B) OR
Answer focus: Why RAID exists + level comparison summary.
Practice from papers (end-of-topic set)
These paper questions map directly to this topic. Solve now, then compare your structure with linked topics.
Summer 2023Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for FCFS and SSTF.
Summer 2023Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for LOOK and SCAN.
Winter 2023Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-LOOK.
Winter 2023Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-SCAN.
Summer 2024Q5(A)
Define RAID. Explain RAID0, RAID1 and RAID2.
Winter 2024Q5(A)
Define RAID. Explain RAID0, RAID1 and RAID2.
Summer 2025Q5(C)
Explain FIFO disk scheduling algorithm with example.
Summer 2025Q5(C) OR
Explain SSTF disk scheduling algorithm with example.
Question Bank Linked Here
Open all questionsSummer 2023Q5(B) OR
Discuss RAID.
Summer 2023Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for FCFS and SSTF.
Summer 2023Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for LOOK and SCAN.
Winter 2023Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-LOOK.
Winter 2023Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-SCAN.
Summer 2024Q5(A)
Define RAID. Explain RAID0, RAID1 and RAID2.
Winter 2024Q5(A)
Define RAID. Explain RAID0, RAID1 and RAID2.
Summer 2025Q5(C)
Explain FIFO disk scheduling algorithm with example.
Summer 2025Q5(C) OR
Explain SSTF disk scheduling algorithm with example.
How to answer linked exam questions
Full question bankSummer 2023 Q5(B) OR
Discuss RAID.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Summer 2023 Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for FCFS and SSTF.
Answer pattern: define briefly, then solve stepwise and show final values/table.
Summer 2023 Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, calculate total movement for LOOK and SCAN.
Answer pattern: define briefly, then solve stepwise and show final values/table.
Winter 2023 Q5(C)
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-LOOK.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Winter 2023 Q5(C) OR
For requests 1,36,16,34,9,12 and current head 11 on 51-cylinder disk, find total movement using C-SCAN.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Summer 2024 Q5(A)
Define RAID. Explain RAID0, RAID1 and RAID2.
Answer pattern: one-line definition, key properties, and one short real-world use case.
Extra clarity files
These are clearly marked additions, separate from source notes.