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OS · Question Set
Virtualisation & OS Case Studies interview questions for placements and exams.
Questions
11
Included in this set
Subject
OS
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Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for OS.
In virtualisation architectures a Type 1 (bare-metal) hypervisor runs directly on the host machine’s hardware, offering better performance and efficiency. A Type 2 hypervisor runs on a host operating system as an application layer, and then hosts guest operating systems. Knowing this distinction is a common interview point.
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Live migration enables moving a virtual machine that is currently running from one physical host to another with minimal or no downtime. It is used for load balancing, maintenance, high availability. Interview questions often test how and why this works.
OS-level virtualisation is the technique where multiple isolated user-space instances (containers or zones) run on a single operating system kernel, sharing that kernel and underlying hardware. For example, technologies like Solaris Zones or OpenVZ implement OS-level virtualisation. Advantages include lightweight operation, near-native performance, fast startup, efficient resource use. Limitations include less isolation compared to full virtual machines (since kernel is shared), and inability to run different OS kernels or completely different operating systems. Demonstrating both sides (advantages and limitations) is key for interview depth.
Resource over-commit means that the hypervisor or virtualisation platform allows virtual machines collectively to hold more CPUs, RAM or storage allocations than the underlying physical host provides, relying on the fact that not all VMs will use their maximum at the same time. This improves utilisation but also introduces risk of contention and performance degradation. Knowing this risk-vs-benefit is useful in interviews.
Nested virtualisation occurs when a virtual machine itself hosts another virtualisation layer (a VM inside a VM). This can be useful for development, testing or cloud provider architectures. Challenges include increased overhead, more complex hardware and hypervisor support (CPU extensions like VT-x/AMD-V must be forwarded), more layers of translation (guest to host), greater resource contention and reduced performance. Discussing real-world scenarios or trade-offs strengthens your answer in interviews.
In practice live migration is used to move running workloads off a host for maintenance without stopping services. While hardware compatibility matters, the key interview point is that migration enables high availability and service continuity. Explaining host compatibility, shared storage, network dependencies adds depth.
Virtualisation introduces additional layers (hypervisor, emulated hardware, translation) which can reduce performance versus native. Overheads include CPU context switches, I/O translation, memory management, device emulation, and increased latency. Recognising these trade-offs is beneficial in interviews.
Virtualisation is the process of creating virtual instances of physical resources — for example servers, storage or networks — so that you can run multiple separate environments on the same hardware. This improves resource utilisation and flexibility.
A virtual machine includes a full guest operating system and virtualised hardware, so each VM is isolated and runs independently. It uses a hypervisor to manage resources. A container, by contrast, shares the host OS kernel but isolates the user-space environment; containers are lighter weight, start faster and use fewer resources. Use-cases: VMs are good when full isolation and different OSs are needed (for instance running Windows and Linux on one host). Containers are ideal for microservices, rapid deployment and when many similar processes need to run in isolation but share host resources. Mentioning the trade-offs (isolation vs lightweight, flexibility vs overhead) is important for interviews.
Virtualised environments introduce security concerns such as VM escape (guest breaking out of its sandbox), hypervisor attacks, sharing of resources causing side-channel leaks, and mis-configuration of virtual networks or snapshots. To mitigate these, OS and virtualisation platform designers adopt measures such as strict isolation between VMs (via hardware support like IOMMU, VT-d), secure hypervisor design, patching and minimal trusted computing base, network segmentation, secure boot, and proper access control. In interviews referencing container vs VM isolation differences and real-world mitigation steps shows your understanding.
When migrating VMs at scale, challenges include compatibility of CPU features between source and target hosts, needing shared storage or having to transfer large amounts of memory state, network connectivity and IP continuity, performance hit and downtime, dependency on hypervisor versions, resource contention during migration and ensuring minimal service disruption. Mitigation includes live migration planning, using abstraction layers, homogeneous hardware clusters or CPU feature masking, shared storage or replication, and scheduling migration during low-utilisation windows. Mentioning real-world constraints and steps to address them enhances your answer.