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1. What is virtualization?
Answer: Virtualization is a technology that creates an abstraction layer on computer hardware, dividing the hardware resources of a single physical computer (such as processor, memory, storage, etc.) into multiple virtual computers (virtual machines, VMs). Each virtual machine can run its own operating system and applications, as if it were an independent computer. This method improves the utilization of hardware resources and is one of the foundational technologies of cloud computing.
2. What are the core advantages of virtualization?
Answer: The core advantages of virtualization lie in the efficient reuse, flexible allocation, and multi-environment isolation of resources through the abstraction of physical resources, significantly improving hardware utilization and reducing operational costs.
3. What are the common types of virtualization?
Answer: Common types of virtualization include server virtualization (e.g., VMware), desktop virtualization (VDI), network virtualization (SDN/Overlay), storage virtualization (storage pools), application virtualization (VMware ThinApp, Sandboxie), and container virtualization (e.g., Docker, containerd), covering the abstraction and isolation of computing, resources, and environments.
4. What is a Hypervisor?
Answer: A Hypervisor (virtual machine monitor) is the core of virtualization technology, a software layer that runs between the physical server and the operating system, allowing multiple virtual machines (virtual operating systems) to run simultaneously on a single physical server, with these virtual machines operating independently and without interference. There are two types of Hypervisors:
- Type 1 (Bare-metal): Runs directly on physical hardware, offering higher performance, commonly used in data centers and server environments, such as VMware ESXi, KVM, Microsoft Hyper-V, etc.
- Type 2 (Hosted): Runs on top of an operating system, suitable for desktop and development testing environments, such as VMware Workstation / VMware Fusion, VirtualBox, Parallels Desktop, etc.
5. What is the difference between a virtual machine (VM) and a physical machine?
Answer: A virtual machine is a computer simulated by software that can run on a physical machine, sharing the physical machine’s hardware resources, while a physical machine is an actual hardware device with independent hardware resources. Physical machines provide higher performance and resource exclusivity, while virtual machines offer better resource utilization and flexibility.
6. What are the typical application scenarios for server virtualization?
Answer: Typical application scenarios for server virtualization include:
- Resource consolidation: Consolidating multiple low-utilization physical servers into a single host, reducing costs and energy consumption.
- Cloud computing (IaaS): Supporting public/private cloud services, achieving elastic resource allocation (e.g., AWS, Azure).
- Development and testing environments: Quickly creating/destroying isolated sandbox environments to enhance development efficiency.
- Disaster recovery: Quickly restoring business through virtual machine snapshots and migrations, reducing downtime risks.
- Load balancing and high availability: Dynamically migrating virtual machines to distribute load and avoid single points of failure.
- Security isolation: Providing independent environments for different applications or tenants (e.g., multi-tenant SaaS).
- Legacy system compatibility: Running legacy systems in a virtual environment to avoid hardware dependencies.
7. What is a vCPU?
Answer: A vCPU (Virtual CPU) is a core concept in virtualization technology, referring to the virtual processor units allocated on a physical server through virtualization software (such as VMware, Hyper-V, KVM, etc.). It is the core resource unit of virtualization technology, allowing virtual machines (VMs) to execute computing tasks as if they were using real physical CPUs, with the underlying physical CPU resources dynamically allocated and scheduled.
8. How is memory virtualization achieved?
Answer: Memory virtualization is achieved through the dynamic mapping of virtual machine memory to physical memory by the Hypervisor, combined with hardware acceleration (such as Intel EPT/AMD RVI) and memory overcommitment technology, to achieve memory isolation and efficient reuse among multiple virtual machines.
9. What is the role of storage virtualization?
Answer: The core role of storage virtualization is to abstract physical storage resources, achieving the following functions:
- Unified management: Integrating dispersed heterogeneous storage devices (such as SAN/NAS/local disks) into a logical resource pool, simplifying operations;
- Flexible allocation: Dynamically allocating storage space on demand (such as thin provisioning), supporting advanced features like snapshots and clones;
- Improved utilization: Eliminating storage silos, reducing redundancy and waste;
- Enhanced availability: Supporting transparent data migration and disaster recovery (such as cross-device replication), reducing business interruption risks.
Essentially, it decouples physical hardware from application needs at the logical layer, achieving efficient, elastic, and automated management of storage resources.
10. What are the core technologies of network virtualization?
Answer: The core technology of network virtualization is to abstract and simulate hardware-level network devices and resources through software, allowing the creation of multiple virtual networks on a single physical network, including the creation of virtual switches, virtual network cards, and virtual routers, using software-defined networking (SDN), enabling virtual machines to communicate with each other through these virtual networks and connect with the physical network.
11. What are the advantages of desktop virtualization (VDI)?
Answer: Desktop virtualization (VDI) achieves unified operations, data locality, and reduced hardware costs through centralized management, security isolation, flexible access (remote/multi-terminal), and dynamic resource allocation, significantly enhancing the security and efficiency of enterprise desktop environments.
12. What is container virtualization?
Answer: Container virtualization is a lightweight technology that achieves process-level isolation by sharing the host machine’s kernel and utilizing namespaces and control groups (Cgroups) (e.g., Docker), providing a fast-deploying, resource-efficient application runtime environment.
13. What is the difference between containers and virtual machines?
Answer: The core difference between containers and virtual machines is that containers share the host OS kernel, achieving lightweight process-level isolation (e.g., Docker), while virtual machines need to simulate complete hardware and run independent OS (e.g., VMware), consuming more resources but providing stronger isolation. Virtual machines simulate a complete operating system and hardware, while containers share the host operating system’s kernel, virtualizing only the software layer. Containers are lighter, start faster, but have less isolation than virtual machines.
14. What is resource overcommitment in virtualization?
Answer: Resource overcommitment in virtualization refers to allocating physical resources (such as CPU, memory, storage) to different application loads (VMs) in a way that exceeds the standard physical resource allocation at the same time, through dynamic scheduling and sharing mechanisms, to improve resource utilization and sharing, but it needs to balance performance risks (such as slowdowns caused by contention).
15. What is live migration?
Answer: Live migration is the transparent migration of a virtual machine from one physical host to another while it is running (zero downtime), allowing for dynamic resource adjustment, load balancing, or hardware maintenance without affecting business continuity.
16. Where might the performance bottlenecks in virtualization be?
Answer: Performance bottlenecks in virtualization may occur in: CPU resource contention, excessive memory allocation, disk I/O bottlenecks, network latency, and hardware emulation overhead.
17. What functions does a virtual switch have?
Answer: The core function of a virtual switch is to enable network communication between virtual machines in a virtualized environment, traffic control (such as VLAN segmentation, QoS), and connecting virtual machines to the physical network, while supporting security policies (such as ACL) and monitoring, ensuring efficient and secure data transmission.
18. What types of RAID are common in storage virtualization?
Answer: Common RAID types in storage virtualization include RAID 0 (striping), RAID 1 (mirroring), RAID 5 (striping with parity), RAID 6 (striping with double parity), and RAID 10 (combination of mirroring and striping).
19. What is QoS (Quality of Service) in virtualization?
Answer: In a virtualization environment, QoS (Quality of Service) refers to prioritizing and limiting the resources (such as bandwidth, CPU, memory) of virtual machines or virtual networks to ensure that critical business applications receive stable performance guarantees.
20. What security risks exist in a virtualization environment?
Answer: The main security risks in a virtualization environment include virtual machine escape (VM escape), cross-VM attacks, resource abuse, Hypervisor vulnerabilities, shared storage data leakage, and side-channel attacks.
21. How to monitor virtual machine performance?
Answer: By regularly collecting and analyzing metrics such as CPU, memory, disk I/O, and network throughput of virtual machines through monitoring platforms, combined with alert strategies to timely identify and locate performance bottlenecks.
22. What is a virtual machine template?
Answer: A virtual machine template is a pre-configured virtual machine image with an operating system, applications, and settings, used for quickly cloning consistent virtual machine instances, such as OVF (Open Virtualization Format) and heat templates in OpenStack.
23. How is high availability (HA) in virtualization achieved?
Answer: By using shared storage and multi-point heartbeat detection, when a physical host fails, virtual machines are automatically migrated or rebuilt to other healthy nodes, ensuring that virtual machine services remain online.
24. What is Nested Virtualization?
Answer: Nested Virtualization is running another layer of Hypervisor within a virtual machine, achieving multi-level virtualization on the same physical host, commonly used in testing and development scenarios, not recommended for production environments.
25. What protocols are used in desktop virtualization?
Answer: Common protocols in desktop virtualization include Microsoft RDP, VMware PCoIP, Citrix ICA/HDX, Red Hat SPICE, and open-source RFB (VNC).
26. What are container orchestration tools?
Answer: Container orchestration tools are systems used for automating the deployment, management, scaling, and networking of containerized applications, such as Kubernetes, Docker Swarm, and Apache Mesos.
27. How is virtualization license management handled?
Answer: Virtualization license management is typically authorized based on the number of physical/virtual CPU cores (Per Core), CPU sockets (Per Socket), or the number of virtual machine instances, and is allocated and tracked through centralized license servers or management platforms.
28. What is NUMA (Non-Uniform Memory Access)?
Answer: NUMA (Non-Uniform Memory Access) is a multi-processor system architecture where each CPU has a low-latency channel for local memory access, while accessing memory from other CPUs incurs higher latency. In use, it is necessary to optimize CPU and memory affinity to enhance performance, such as binding the CPU and memory allocation of virtual machines or processes to the same NUMA node (CPU & memory affinity), enabling NUMA-aware schedulers, and adjusting the NUMA policies of the operating system or Hypervisor to reduce cross-node memory access latency.
29. What types of virtual disks are there?
Answer: There are three main types of virtual disks:
- Thick Provisioned: All physical storage space is pre-allocated, ensuring performance but occupying actual capacity.
- Thin Provisioned: Storage is allocated on demand, initially occupying little space, dynamically expanding, saving space.
- Differencing/Delta Disk: Records increments on top of a base template, facilitating rollback and version management.
30. What is VxLAN in network virtualization?
Answer: VxLAN (Virtual eXtensible LAN) is an overlay protocol that encapsulates Layer 2 networks over Layer 3 physical networks using UDP tunneling technology, breaking the traditional VLAN limit of 4094 (supporting over 16 million virtual network identifiers, VNIs), achieving large-scale virtual network isolation and flexible networking across data centers.
31. What backup methods are available in virtualization?
Answer: Backup methods in virtualization include full/incremental backups, snapshots (such as virtual machine snapshots), storage-based replication, agentless backups, and application-consistent backups (such as database quiescence), ensuring data integrity and enabling rapid recovery through multi-layered technologies.
32. What is SR-IOV (Single Root I/O Virtualization)?
Answer: Directly assigning physical network cards to virtual machines, bypassing the Hypervisor to enhance I/O performance.
SR-IOV stands for Single Root I/O Virtualization, a technology that virtualizes physical devices (such as network cards) into multiple independent virtual functions (VFs) through hardware, allowing virtual machines to directly use hardware network card resources through allocated VFs, bypassing the Hypervisor layer, significantly improving I/O performance and reducing latency.
33. What is the relationship between containers and microservices?
Answer: Containers are a way to implement microservices architecture, providing a simple, efficient, and scalable way to run microservices. Containers provide a standard runtime environment for microservices, allowing them to be deployed and run independently. By using containers, rapid deployment, scaling, and migration of microservices can be achieved, while the automated management features of container clouds also simplify the operations of microservices.
34. What resource scheduling strategies exist in virtualization environments?
Answer: Resource scheduling strategies in virtualization environments mainly include: dynamic allocation (CPU/memory), load balancing, share allocation, priority scheduling, resource reservation/limits (Reservation/Limit), and QoS-based auto-scaling, aimed at optimizing resource utilization and ensuring the performance of critical business applications.
35. What is vMotion?
Answer: vMotion is VMware’s live migration technology for virtual machines, allowing the migration of running virtual machines across physical hosts without interrupting services, achieving dynamic resource optimization and zero downtime for hardware maintenance.
36. What is the difference between NAS and SAN in storage virtualization?
Answer: In storage virtualization, NAS (Network Attached Storage) provides shared storage pools through file-level protocols (such as NFS/SMB), supporting multi-node collaborative access; SAN (Storage Area Network) provides high-performance virtual disks based on block-level protocols (such as iSCSI/FC), specifically for low-latency, high-throughput critical business applications. Both are managed through a virtualization layer but are suitable for different scenarios.
37. What is a thin client in desktop virtualization?
Answer: A thin client in desktop virtualization is a lightweight terminal device that relies on backend servers to perform computing tasks, handling only user input and display output, with no local storage or complex computing capabilities, achieving low maintenance costs and centralized data control.
38. What are the key points for compatibility testing in virtualization?
Answer: Compatibility testing in virtualization should focus on verifying hardware (such as CPU virtualization instruction support), compatibility of host/client operating systems, application functionality and performance (including drivers/dependencies), cross-platform migration capabilities (such as vMotion), and resource allocation strategies, ensuring stable operation of the virtualization environment and efficient resource utilization.
39. What are the differences between Namespace and Cgroups in containers?
Answer: The Namespace in containers is responsible for resource isolation (such as processes, networks, file systems), while Cgroups is responsible for resource limitation (such as CPU/memory quotas). The former addresses “visibility isolation,” while the latter addresses “usage control,” working together to ensure that the container environment is both independent and resource-constrained.
40. What is the role of port groups in virtual switches?
Answer: The role of port groups in virtual switches is to provide a logical grouping for virtual machines to offer unified network configuration (such as VLAN, security policies, and traffic control rules), simplifying network management for multiple virtual machines and ensuring policy consistency.
41. What disaster recovery solutions exist in virtualization?
Answer: Disaster recovery solutions in virtualization mainly include: local rapid recovery based on snapshots/replication, cross-site disaster recovery (such as VMware SRM, active-active in the same city, remote disaster recovery), high availability clusters (HA), and cloud disaster recovery (such as AWS DRS), ensuring business continuity through multi-layer redundancy and automated switching.
42. What is Overcommit?
Answer: Overcommit is the logical allocation of resources in virtualization that exceeds the total physical resources (such as CPU, memory, storage) through dynamic allocation, based on the assumption of “non-peak simultaneous operation” to enhance utilization, but it is necessary to be cautious of performance degradation risks caused by resource contention.
43. What is the layered technology of storage virtualization?
Answer: The layered technology of storage virtualization automatically allocates data to different performance tiers of storage media (such as SSD, HDD, tape) based on data access frequency (cold/hot data), achieving high-performance resource focus on hot data while reducing storage costs for cold data.
44. How to implement firewall deployment in network virtualization?
Answer: Firewall deployment in network virtualization can be achieved through distributed virtual firewalls (such as VMware NSX, OpenStack Security Group) or NFV technology (virtualized firewall instances), embedding security policies at the virtual switch or Hypervisor layer, dynamically controlling east-west (internal) and north-south (external) traffic, and supporting automated policy orchestration and micro-segmentation.
45. What is offline mode in desktop virtualization?
Answer: Offline mode in desktop virtualization allows continued access to the virtual desktop environment through local caching or temporary virtual machines in a disconnected environment, automatically synchronizing data updates once the network is restored, ensuring business continuity in mobile or weak network scenarios.
46. What is a container image repository?
Answer: A container image repository is a platform for centralized storage, management, and distribution of container images (such as Docker Hub, Harbor), providing version control, access permission management, and image pull/push functions, supporting team collaboration and continuous delivery processes.
47. What performance optimization tools are available for virtualization?
Answer: Common performance optimization tools for virtualization include VMware ESXTOP for real-time monitoring of ESXi host performance metrics (CPU, memory, network, storage), Windows Performance Monitor (PerfMon) for detailed tracking of Windows virtual machine metrics, Prometheus + Grafana for visualization and alerting, virt-top for monitoring virtual machine performance, Red Hat Insights for KVM and OpenShift optimization recommendations, and APM tools like Dynatrace and AppDynamics for end-to-end application performance analysis.
48. What is DRS (Distributed Resource Scheduler)?
Answer: DRS (Distributed Resource Scheduler) is an automation engine in virtualization clusters that monitors host and virtual machine loads in real-time and dynamically balances or migrates virtual machines between hosts based on preset policies to optimize resource utilization and performance.
49. What risks are associated with snapshot rollback in storage virtualization?
Answer: The risks associated with snapshot rollback in storage virtualization mainly include data inconsistency (such as unquiesced application states), snapshot chain breaks leading to subsequent snapshot failures, performance drops during rollback (I/O blocking), and storage space exhaustion (due to long dependency chains). Most importantly, there is a risk of losing data modifications made after the rollback point, requiring the use of application consistency agents and periodic snapshot cleanup to mitigate risks.
50. How is DHCP service configured in virtual networks?
Answer: The DHCP service in virtual networks is configured by creating virtual DHCP server instances in virtualization platforms (such as VMware ESXi, OpenStack Neutron) or integrating physical DHCP, configuring address pools, gateways, subnets, and lease parameters, and binding them to the target virtual network or port group, achieving automated IP allocation and network topology adaptation.
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