11.1 Virtualization Concepts and Techniques

Virtualization is a game-changer in modern computing. It lets multiple virtual machines share one physical machine, making better use of hardware and saving costs. This tech enables efficient server consolidation, quick deployment, and seamless migration of workloads.

Understanding virtualization is key to grasping modern computer architecture. It involves hypervisors managing virtual machines, each with its own operating system. Full virtualization simulates hardware completely, while paravirtualization modifies guest OSs for better performance. Both have pros and cons.

Virtualization in modern computing

Definition and role

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• Virtualization allows multiple virtual machines (VMs) to run on a single physical machine, sharing hardware resources
• Enables efficient utilization of hardware by allowing multiple operating systems and applications to run concurrently on a single physical server
• Provides isolation between VMs, ensuring independent and secure operation without interference
• Facilitates server consolidation, reducing the number of physical servers required and leading to cost savings (hardware, energy, maintenance)
• Enables rapid provisioning and deployment of VMs, allowing for increased agility and flexibility in managing computing resources
• Supports live migration of VMs between physical hosts, enabling load balancing, high availability, and maintenance without downtime

Benefits and use cases

• Improved resource utilization and efficiency by consolidating multiple workloads on a single physical machine
• Enhanced reliability and availability through live migration and high availability features (VMware vSphere, Microsoft Hyper-V)
• Simplified management and maintenance of computing resources through centralized control and automation
• Increased agility and flexibility in provisioning and scaling resources based on demand
• Cost savings in terms of hardware acquisition, energy consumption, and data center space

Components of a virtualized system

Hypervisor (Virtual Machine Monitor)

• Software layer that manages and coordinates the execution of multiple VMs on a single physical machine
• Type 1 (Bare-metal) Hypervisor runs directly on the host's hardware, providing better performance and security (VMware ESXi, Microsoft Hyper-V)
• Type 2 (Hosted) Hypervisor runs as a software layer on top of an existing operating system (VMware Workstation, Oracle VirtualBox)
• Responsible for allocating hardware resources to VMs and managing their execution

Virtual Machines (VMs) and Guest Operating Systems

• VMs are software-based emulations of physical computers, each running its own operating system and applications
• Guest Operating System is the OS that runs within each VM, which can be different from the host operating system
• VMs are isolated from each other, providing security and fault tolerance
• Multiple VMs can run concurrently on a single physical machine, sharing hardware resources

Virtual Hardware and Networking

• Virtual Hardware includes emulated components (virtual CPUs, memory, storage devices, network interfaces) assigned to each VM
• Allows VMs to operate as if they have dedicated hardware resources
• Virtual Network enables communication between VMs and the host, as well as between VMs on the same or different physical machines
• Supports various network configurations (bridged, NAT, host-only) to meet different networking requirements

Full vs paravirtualization

Full Virtualization

• Provides a complete simulation of the underlying hardware, allowing unmodified guest operating systems to run within VMs
• Requires hardware-assisted virtualization features (Intel VT-x, AMD-V) for efficient execution
• Offers better compatibility with a wide range of guest operating systems
• Can incur higher performance overhead due to the need for binary translation of privileged instructions

Paravirtualization

• Involves modifying the guest operating system to be aware of the virtualized environment and communicate directly with the hypervisor
• Requires changes to the guest OS kernel to replace privileged instructions with hypercalls
• Provides better performance compared to full virtualization, as the guest OS cooperates with the hypervisor, reducing the need for binary translation
• Offers improved scalability and resource utilization
• Limited compatibility with guest operating systems, as they need to be modified to support paravirtualization (Xen, Oracle VM)

Benefits and challenges of virtualization

Benefits

• Improved resource utilization and efficiency by consolidating multiple workloads on a single physical machine
• Enhanced reliability and availability through live migration and high availability features
• Simplified management and maintenance of computing resources through centralized control and automation
• Increased agility and flexibility in provisioning and scaling resources based on demand
• Cost savings in terms of hardware acquisition, energy consumption, and data center space

Challenges and considerations

• Performance overhead, particularly for I/O-intensive workloads, due to the additional layer of abstraction introduced by virtualization
• Increased complexity in managing and orchestrating large-scale virtualized environments
• Security concerns, such as the potential for hypervisor vulnerabilities and the need for proper isolation between VMs
• Licensing and support considerations for proprietary virtualization platforms (VMware, Microsoft)
• Compatibility issues with certain hardware devices or legacy applications that may not work well in virtualized environments