Introduction to Virtualization

What is Virtualization？

Virtualization is a resource management technology that abstracts and transforms the physical resources of a computer, such as servers, networks, memory, and storage, allowing these resources to be used in a more flexible manner. This abstraction breaks down the barriers between physical hardware components, enabling users to utilize resources in ways that are not limited by the existing architecture, geographical location, or specific physical devices. Virtualization creates an isolation layer that separates the hardware from the upper-layer applications, allowing multiple logical applications to run on a single hardware resource.

Types of Virtualization

• Server Virtualization: Allows multiple operating systems to run simultaneously on a single physical server.
• Application Virtualization: Enables applications to run independently of the underlying operating system.
• Presentation Layer Virtualization: Provides remote access to application interfaces.
• Desktop Virtualization: Delivers personal desktop environments remotely.

Common Virtualization Technologies

• Memory Virtualization: Managed by the vmkernel, each virtual machine (VM) has its own independent and contiguous addressable virtual memory space.
• Disk Virtualization: Utilizes VMDK (Virtual Machine Disk) file format to represent virtual disks.
• Network Virtualization: Implemented through virtual switches.

VMware x86 Server Virtualization

• Compute Power: CPU and memory virtualization.
• Storage: VMFS (Virtual Machine File System) support.
• Networking: Virtual switch support.

Server Virtualization Approaches

• Hosted Architecture:
• Installed on top of an existing operating system.
• Good compatibility but lower performance and limited functionality.
• Bare Metal Architecture:
• Installed directly on the hardware without an underlying OS.
• Better performance and advanced features, but higher hardware compatibility requirements.

Benefits of Using Virtual Machines

• Maximized Resource Utilization: Efficient use of physical server resources.
• Easier Access to Computing Resources: Simplified resource acquisition.
• Hardware Agnostic: Easy migration and protection since VMs are just files.
• Extended Lifecycle: Not tied to specific hardware, leading to a longer lifespan.
• Dynamic Resource Allocation: Easy to change resource assignments based on demand.
• Advanced Features: Such as live data and VM migration, high availability, and automatic resource allocation.
• Cost Reduction: Lower overall costs, including management and maintenance.

vSphere Basic Architecture

• Resource Sharing: Physical resources like CPU, memory, network, and storage are shared among multiple VMs.
• CPU Virtualization:
• LCPU (Logical CPU): Represents the available physical resources.
• vCPU (Virtual CPU): The virtualized CPU managed by the vmkernel.
• vmkernel: Responsible for CPU resource scheduling.
• Memory Virtualization:
• Controlled by the vmkernel, each VM has its own independent and contiguous virtual memory space.
• Uses various techniques to optimize memory usage, and can use disk storage as swap space when physical memory is insufficient.
• Network Virtualization:
• Implemented through virtual switches.
• Connects VMs, vmkernel, and external physical networks, operating at the second layer.
• Virtual NIC (vNIC): Network interface card within the VM.
• vmkernel NIC: For vmkernel communication with the external network.
• Physical NIC: Connects to the physical network.
• Storage Virtualization:
• Uses VMDK files to encapsulate virtual disks.
• Multiple ESXi hosts can access shared storage.
• Each VM’s virtual disk is stored as a VMDK file, and each VM consists of a set of files in its own directory.
• The VM’s file system is not visible to the ESXi host.

vSphere and Cloud Computing

• Foundation: Virtualization is the foundation of cloud computing.
• Platform Support: Supports various cloud platforms like VMware vRealize and OpenStack.
• Cloud Environments: Suitable for private, public, and hybrid cloud deployments.

ESXi Basic Structure

• Core Component: VMware ESXi is the primary hypervisor, installed directly on the physical server.
• Installation Options: Can be installed on local hard drives, SAN, USB/SD cards, or even in memory.
• Advantages: Compact architecture, enhanced security, simplified deployment, and streamlined update processes.

ESXi Host Management

• Standalone Management: Suitable for initial setup or troubleshooting.
• vCenter Server Management: Centralized management for multiple ESXi hosts, providing advanced features and integration with third-party plugins.

vCenter Server

• Definition: vCenter Server is a service for centralized management of enterprise virtualization environments.
• Functions: Provides a unified management interface, supports VM migration, distributed services, and other advanced features.
• Logical Components: Includes database servers, SSO (Single Sign-On) components, inventory services, and more.
• Extensible Components: Additional management tools, such as cloud platform management and site recovery management, can be installed as needed.

VMware Virtual Machines and Management

• Virtual Machines: A logical computer consisting of a set of discrete files, such as .vmx, .nvram, .vmdk, etc.
• Templates: Used for rapid deployment of new VMs, created by converting or cloning existing VMs.
• Cloning: Creates an exact copy of a VM, useful for backup or testing.
• Migration:
• Cold Migration: VM is powered off or suspended during the migration.
• vMotion: Live migration of a running VM between hosts.
• Storage vMotion: Live migration of a VM’s storage while the VM remains running.

VM Snapshots

• Purpose: To preserve the state of a VM for rollback.
• Mechanism: When a snapshot is taken, a state file is created, and the original disk becomes read-only, with changes written to a new delta disk.
• Considerations: Snapshots are a temporary fault-tolerance solution and should not replace regular backups.

VMware Availability and Scalability

• High Availability (HA): Automatically restarts VMs on another host in case of a host failure, ensuring minimal downtime.
• Fault Tolerance (FT): Provides zero downtime and zero data loss by maintaining a secondary VM that takes over immediately if the primary VM fails.
• Distributed Resource Scheduler (DRS): Dynamically balances compute resources across a cluster, ensuring optimal performance and resource utilization.

Virtualization not only enhances the efficiency and flexibility of IT resources but also provides robust disaster recovery and business continuity capabilities, making it an essential technology for modern data centers.