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Among all virtualization technologies, server virtualization is the earliest applied, so people often equate server virtualization with the concept of virtualization, or use the two interchangeably. Server virtualization logically divides the server hardware, running independent operating systems within each logical unit, which do not interfere with each other and share the entire hardware resources. Based on implementation principles, server virtualization can be divided into virtualization based on x86 architecture CPUs, virtualization based on RISC architecture, and virtualization based on operating systems.
(1) Virtualization Technology Based on x86 Architecture CPUs
Mainstream CPU manufacturers such as Intel and AMD have added virtualization instructions to their CPU instruction sets, thereby enhancing support for virtualization. The instructions generated by virtual machines can run directly without conversion, greatly improving the overall operating efficiency of virtual machines and promoting the virtualization process from the hardware level. CPUs with virtualization instruction sets from Intel are marked as Intel VT, while those from AMD are marked as AMD VT.
(2) Virtualization Technology Based on RISC Architecture
The small machines referred to here are servers that use RISC architecture. Compared with x86 architecture, servers based on RISC architecture have embedded virtualization technology in both the CPU and operating system, achieving a more comprehensive implementation. IBM is the leader and pioneer of virtualization technology under this architecture. On p-series servers and the AIX operating system, IBM announced that multiple partitions can run independently within a single system, each running an independent operating system, supported by its dynamic logical partitioning (LPAR) technology. The CPU’s support for virtualization can be further subdivided from the early “grain” partitioning to the current micro-partitioning, supported by the AIX system, allowing for the operation of more partitions than the number of physical processors.
(3) Operating System-Based Virtualization
Virtualization software runs within the operating system to achieve logical structures of virtualization, all of which are managed by the operating system, similar to how applications run on the operating system. Operating system-based virtualization is usually applied in testing environments, allowing for complex logical structures to be realized and simulated on a single physical resource through simple deployment, saving time and effort while reducing investment.
(4) Introduction to Major Products
VMware has a high market share in the field of server virtualization and is one of the manufacturers with the most diverse product lines. Microsoft’s Hyper-V is a rising star, and with the dominance of Windows 2008 and Windows 2012 on the x86 architecture, Hyper-V’s market share has rapidly increased. Xen is an open-source virtualization technology based on the Linux platform, classified as a paravirtualization technology.
1. VMware VMware is one of the main manufacturers in the field of server virtualization, with a rich product line covering areas from infrastructure to high availability.
VMware consists of two main components: VMware vCenter and VMware vSphere.
VMware vCenter is the centralized management center for virtualization, capable of managing hundreds of ESX servers and thousands of virtual machines, providing advantages such as operational automation, resource optimization, and high availability. vCenter offers a single Windows management client to manage all tasks, known as the vSphere Client. Users can configure, start, stop, delete, relocate, and remotely access virtual machines using a keyboard and mouse. The vSphere Client can also be used in conjunction with web browsers to access virtual machines from any networked device. The browser-based client allows users to easily access virtual machines as if sending a bookmark URL. Client user programs can access the VMware vSphere data center through a vCenter interface layer, using either a GUI (such as vSphere Client or vSphere Web Client) or command-line interface and software development tools.
VMware vSphere is the virtualization platform system, including infrastructure services and application services. Infrastructure services mainly include virtual computers (vComputer), virtual storage (vStorage), and virtual network (vNetwork) services, which can virtualize, aggregate, and allocate hardware or infrastructure resources. Application services are a set of services used to ensure application availability, security, and scalability. The main function of VMware vSphere is to separate applications and operating systems from the underlying hardware, composed of numerous components that undertake various functions of virtualization. The main modules of VMware vSphere are introduced below:
(1)ESX: ESX is the core component of VMware vSphere. As VMware’s underlying virtualization system, ESX is installed directly on the hardware or “bare metal” of various host servers providing resources for the virtual infrastructure, creating multiple VMs (virtual machines). After installing operating systems on these virtual machines, they become virtual servers capable of providing various application services. ESX creates a solid virtualization layer, allowing multiple secure, portable virtual machines to run in parallel on one (or a group of) physical servers. ESXi is an upgraded version of ESX, and versions above ESXi 5.0 have replaced ESX.
(2)Virtual SMP: With Virtual SMP, a single virtual machine can simultaneously use multiple physical processors or CPUs in the host server, enhancing the performance of the virtual machine. Virtual SMP can assist in scheduling non-idle virtual processors while allowing processor overload. By canceling calls to idle virtual processors within the operating system running inside the virtual machine, they can be reallocated to other tasks. Virtual SMP periodically moves tasks being processed among available processors to rebalance workloads. VMware also provides a unique feature, allowing Virtual SMP to support most processor-intensive enterprise applications (such as databases, ERP, and CRM) virtualization.
(3)VMFS: VMFS is the file system for virtual machines, where virtual machines are fully encapsulated in virtual disk files, which can be stored either locally on ESX or centrally stored on shared SAN, NAS, or iSCSI storage. Centralized storage is more common in enterprise environments, allowing other ESX to access shared SAN, NAS, or iSCSI storage and Virtual Machine File System (VMFS) to access each virtual machine centrally. This configuration allows multiple ESX in the resource pool to access the same files in parallel to boot and run virtual machines and effectively virtualize virtual machine storage.
(4)VMotion: VMotion supports real-time migration of virtual machines between hosts. As a key component of a dynamic, automated, and self-optimizing data center, VMotion allows for the real-time migration of running virtual machines between physical servers while avoiding downtime, ensuring continuous service supply and processing integrity. With virtual machine live migration technology, companies do not need to interrupt business operations during hardware maintenance. VMotion also allows for continuous automatic optimization of virtual machines within resource pools, maximizing hardware utilization, flexibility, and availability.
(5)DRS: DRS (VMware distributed resource scheduler) works in conjunction with VMware vSphere to continuously and automatically balance the workloads of virtual machines within the same cluster in the virtual infrastructure. When a virtual machine is first started in a cluster, DRS automatically identifies an ESX host with sufficient resources to run that virtual machine. If the selected host’s situation changes, such as increased activity from other virtual machines, preventing the virtual machine from achieving minimum resource allocation guarantees, DRS will detect this situation and search for a backup ESX host within the cluster that can meet the resource allocation needs of that virtual machine. DRS will then use VMotion to automatically migrate the virtual machine to the new host, ensuring that user operations and applications are not affected. This way, all server workloads in the virtual infrastructure can achieve continuous balance. DRS operates through the ESX Local Scheduler and vCenter Global Scheduler. The ESX Local Scheduler decides which processors in the host should be used for virtual machine execution based on the current workload, and whenever it finds that other host processors can provide more capacity, it will reallocate the virtual machine, potentially reassigning it every few milliseconds. In contrast, the vCenter Global Scheduler continuously evaluates the best placement for virtual machines across the entire cluster where the ESX host resides.
(6)HA: HA (high availability) provides easy-to-use, cost-effective high availability features for applications running in virtual machines. The absence of an ESX host due to hardware failure is no longer a catastrophic event, but simply means a reduction in the resource pool available to the cluster. In this case, HA reallocates resources for the virtual machines on the failed host to other ESX hosts in the cluster and restarts those virtual machines, while the vCenter Global Scheduler determines the best placement for these virtual machines to meet resource demands.
(7)Consolidated Backup: VMware Data Recovery is a backup solution provided by VMware in vSphere Essentials Plus and above versions, and it is a backup agent offered by VMware across all versions of vSphere. Consolidated Backup performs backup operations without using the local area network through an easy-to-use centralized tool, retaining file-level visibility. Consolidated Backup will create snapshots for running virtual machines after stopping applications within the virtual machines, thus processing backup work centrally on disk to ensure file system consistency. Then, a Windows backup agent server mounts these virtual disk snapshots, which can use standard backup agents to store backups on tape or disk devices. Consolidated Backup is pre-integrated with commonly used backup utilities and provides pre-processing and post-processing scripts, making it easy to implement without any additional preparation. Consolidated Backup runs transparently without interrupting the activities of virtual machines. The backup processing occurs outside the ESX host, so it does not impact the CPU and network resources required by critical applications inside the machine. There are no system interruptions during backups, nor does it affect production servers. Since Consolidated Backup only requires running one backup agent on the proxy server (instead of each virtual machine), it reduces the number of required backup agent licenses and improves manageability. Using a proxy server also reduces the load on ESX, allowing ESX to run more virtual machines on the same physical server.
2. Microsoft Hyper-V: In 2003, Microsoft acquired Connectix, which had launched the Virtual PC software, and subsequently launched Virtual Server virtualization software, marking the beginning of Microsoft’s virtualization journey.
In 2008, the latest virtualization product, Hyper-V, was launched. Hyper-V is a hypervisor (virtual machine monitor) with the development code name Viridian, primarily designed to manage and schedule the creation and operation of virtual machines and provide virtualization of hardware resources. Hyper-V is Microsoft’s latest server virtualization solution integrated with Windows Server 2008 upon its release.
The essence of Hyper-V is a VMM (virtualization management program), which differs from the previous Virtual Server series products from Microsoft, as it is closer to the hardware, similar to VMware’s ESX Server series. In fact, Hyper-V is Microsoft’s first bare-metal virtualization product.
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