🔒 Pro · Component 1 · 1.1 Input, Output and Storage
1.1.3c Cloud and Virtual Storage
OCR H446 · A Level Computer Science · ~11 min read
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Cloud Storage
Cloud storage stores data on remote servers operated by a third-party provider, accessed over the internet. Users rent storage capacity rather than owning physical hardware. Examples: Google Drive, Microsoft OneDrive, Amazon S3, Dropbox.
Advantages of cloud storage:
Accessibility: data is accessible from any device with an internet connection, from anywhere in the world.
Scalability: storage can be expanded (or reduced) on demand without purchasing new hardware.
Automatic backup and redundancy: providers typically store multiple copies of data across geographically distributed data centres, protecting against data loss from hardware failure.
No hardware maintenance: the provider handles hardware, firmware updates, cooling, and physical security.
Collaboration: multiple users can access, share, and simultaneously edit files stored in the cloud.
Reduced capital expenditure: businesses pay an ongoing subscription (operating expenditure) rather than a large upfront hardware investment.
Disadvantages of cloud storage:
Dependency on internet: without a reliable internet connection, cloud data is inaccessible.
Security and privacy risks: data is held by a third party; risks of data breaches, unauthorised access, government surveillance, or the provider going out of business.
Ongoing cost: subscription fees accumulate over time and can exceed the cost of local hardware for large organisations.
Latency: internet-based access is slower than accessing local storage.
Data sovereignty: data may be stored in servers in different countries, subject to different legal jurisdictions (e.g. GDPR implications for EU data stored in the US).
Virtual Storage
Virtual storage (also called virtualised storage or a Storage Area Network, SAN) abstracts physical storage resources and presents them to users or applications as a single, unified storage pool. The physical underlying storage (multiple HDDs, SSDs, etc.) is hidden from the user.
How virtual storage works:
A virtualisation layer (software or firmware) maps logical storage addresses presented to applications to physical locations on the underlying storage devices.
Multiple physical drives can appear as one large virtual drive.
Physical drives can be added, removed, or replaced without interrupting running applications (live migration).
Storage can be allocated dynamically to VMs (virtual machines) or applications as needed.
Benefits of virtual storage:
Flexibility: storage capacity can be provisioned (allocated) to applications/VMs without physically adding hardware.
Improved utilisation: physical storage is pooled and shared efficiently; unused capacity in one area can be reassigned to another.
Easier management: administrators manage one logical storage pool rather than many individual drives.
Better redundancy: data can be mirrored across multiple physical devices transparently.
RAID (Redundant Array of Independent Disks)
RAID is a technique that combines multiple physical disks into a logical unit. Different RAID levels offer different tradeoffs between performance, capacity, and fault tolerance.
RAID Level
Description
Min Disks
Pros
Cons
RAID 0 (Striping)
Data split across all disks; no redundancy
2
Maximum performance; full capacity used
One disk failure loses all data
RAID 1 (Mirroring)
Identical copy on every disk
2
Excellent redundancy; easy recovery
50% capacity overhead
RAID 5 (Striping with parity)
Data and parity distributed across all disks
3
Good performance and redundancy; can tolerate 1 disk failure
Reduced write speed; 1 disk capacity used for parity
RAID 10 (1+0)
Mirrored pairs that are then striped
4
High performance + redundancy
50% capacity overhead
Local vs Cloud vs Virtual Storage Comparison
Feature
Local Storage
Cloud Storage
Virtual Storage
Location
On-site physical device
Remote (internet)
Abstracted pool (on-site or remote)
Access speed
Fastest
Internet-limited
Depends on underlying hardware
Scalability
Manual hardware addition
Instant on-demand
Flexible pooling
Cost model
One-time capital cost
Ongoing subscription
Infrastructure cost + management software
Availability risk
Single point of failure (unless RAID)
Internet dependency
Depends on configuration
Exam tip: Cloud storage questions typically ask for advantages AND disadvantages — always include security/privacy, internet dependency, and scalability in your answer. Specify it is a third-party provider storing data.
Exam tip: Know RAID 0, 1, and 5 — their mechanisms, minimum disk count, and the tradeoff between redundancy and capacity. RAID 1 = mirroring (2 disks, 50% overhead); RAID 5 = parity across all disks (min 3, tolerates 1 failure).
⚠ Common Mistakes
Saying cloud storage is always faster — cloud access depends on internet bandwidth; local storage is always faster for latency.
Confusing RAID 0 and RAID 1 — RAID 0 has no redundancy (striping only); RAID 1 mirrors data (redundancy but 50% capacity waste).
Saying cloud storage removes all security risks — it introduces new risks (third-party breaches, government access, data sovereignty).
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Worksheet — 1.1.3c Cloud and Virtual Storage
8 questions · 20 marks · instantly marked
Q1Describe what cloud storage is and explain two advantages it offers a small business compared to maintaining local file servers.[4 marks]
✓ Mark scheme
Cloud storage: data is stored on remote servers operated by a third-party provider and accessed over the internet [1]. Any two advantages from: no hardware maintenance required — the provider manages hardware/cooling/security [1]; scalability — storage can be expanded on demand without purchasing hardware [1]; automatic redundancy — provider typically stores multiple copies across data centres reducing risk of data loss [1]; accessibility — data accessible from any device/location with internet [1]; reduced upfront capital cost — pay subscription (opex) rather than large hardware investment [1].
Q2Explain two risks or disadvantages associated with storing sensitive business data in cloud storage.[4 marks]
✓ Mark scheme
Any two risks, each with explanation: security/privacy — data is held by a third party which may experience a data breach or be compelled to hand data to government authorities [1+1]; internet dependency — without a reliable internet connection cloud data is inaccessible, causing disruption [1+1]; data sovereignty — data stored in foreign jurisdictions may be subject to different legal protections (e.g. GDPR compliance issues) [1+1]; ongoing cost — subscription fees accumulate and may exceed local hardware costs for large organisations [1+1].
Q3Explain what RAID 1 is, how many physical disks are required as a minimum, and give one advantage and one disadvantage compared to a single disk.[4 marks]
✓ Mark scheme
RAID 1 (mirroring): all data is written simultaneously to two (or more) identical disks so each is an exact copy of the other [1]; minimum 2 physical disks [1]; advantage: if one disk fails the system continues operating using the mirror disk with no data loss [1]; disadvantage: the usable storage capacity is halved because every piece of data must be stored twice (50% overhead) [1].
Q4Compare RAID 0 (striping) and RAID 5 (striping with parity) in terms of performance, redundancy, and the minimum number of disks required.[4 marks]
✓ Mark scheme
RAID 0 requires minimum 2 disks; RAID 5 requires minimum 3 disks [1]; both stripe data across disks for improved read/write performance [1]; RAID 0 provides no redundancy — if any single disk fails, all data is lost; RAID 5 stores distributed parity information across all disks so the system can recover from any single disk failure [1]; in RAID 5, the capacity equivalent to one disk is used for parity, so overall usable capacity = (N-1) disks' worth of storage [1].
Q5Explain what virtual storage is and describe one benefit it offers compared to managing individual physical storage drives directly.[3 marks]
✓ Mark scheme
Virtual storage abstracts physical storage devices behind a virtualisation layer, presenting them as a unified logical storage pool [1]; the physical underlying hardware is hidden from applications and users [1]; any one benefit: storage can be provisioned to VMs/applications dynamically without physical reconfiguration [1] / drives can be added or replaced without downtime (live migration) [1] / improved utilisation as unused capacity in one area can be reassigned to another [1].
Q6A hospital is considering moving patient records to cloud storage. Give two reasons why this may raise legal or ethical concerns.[2 marks]
✓ Mark scheme
Any two: data sovereignty — patient data stored on servers in another country may be subject to different data protection laws, potentially violating GDPR [1]; security risk — highly sensitive personal health data stored with a third party is a target for hackers; a breach could expose confidential patient records [1]; third-party access — the cloud provider and potentially government authorities could access patient records without the hospital's or patients' consent [1].
Q7A server uses RAID 5 with 5 disks, each 4 TB. Calculate the total usable storage capacity.[2 marks]
✓ Mark scheme
RAID 5 uses the equivalent of one disk's capacity for parity [1]; usable capacity = (5−1) × 4 TB = 4 × 4 TB = 16 TB [1].
Q8Explain what is meant by 'data sovereignty' in the context of cloud storage and why it is a concern for organisations operating in the EU.[2 marks]
✓ Mark scheme
Data sovereignty refers to the principle that data is subject to the laws of the country where it is physically stored [1]; for EU organisations, if personal data is stored on servers located outside the EU (e.g. in the US), it may not receive the same legal protections as under GDPR (General Data Protection Regulation), potentially breaching EU data protection law [1].
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Mini Test — 1.1.3c Cloud & Virtual Storage
10 questions · 10 marks · 10 minutes
5 MCQ + 5 short answer
⏱10:00
10 marks
Section A — Multiple Choice
Q1Which RAID level provides no redundancy but maximum performance and capacity?
Q2Cloud storage is accessed via:
Q3A RAID 5 array with 4 disks of 2 TB each has a usable capacity of:
Q4Which cloud storage concern relates to data being stored in servers in another country under different legal protections?
Q5Virtual storage differs from cloud storage because:
Section B — Short Answer
Q6State one advantage of cloud storage related to business continuity.
Mark schemeThe provider stores multiple copies across geographically distributed data centres, so if one data centre fails, data remains available from another location. [1 mark]
Q7State what RAID stands for.
Mark schemeRedundant Array of Independent Disks. [1 mark]
Q8State one disadvantage of cloud storage compared to local storage regarding access speed.
Mark schemeCloud storage access speed is limited by internet connection bandwidth and latency; local storage is accessed directly and is always faster. [1 mark]
Q9What is the minimum number of disks required for RAID 5?
Mark scheme3 disks. [1 mark]
Q10State one benefit virtual storage provides over managing individual physical drives directly.
Mark schemeAny one of: storage can be provisioned dynamically to applications/VMs without physical reconfiguration [1] / drives can be added/replaced without downtime [1] / improved utilisation by pooling capacity across devices [1].