VMware vSphere® is an infrastructure virtualization suite that provides virtualization, management, resource optimization, application availability, and operational automation capabilities in an integrated package.
vSphere virtualizes and aggregates the underlying physical hardware resources across multiple systems and provides pools of virtual resources to the datacenter.
In addition, vSphere provides a set of distributed services that enable detailed, policy-driven resource allocation, high availability, and scalability of the entire virtual datacenter.
Physical Infrastructure
Traditionally, operating systems and software run on a physical computer. Several challenges exist to running a large number of physical servers in a datacenter. The model is not flexible and can be inefficient. The planning and cost of proper infrastructure (square footage, rack space, power, cooling, cabling, and server provisioning) are but a few of the problems that IT staff must address. Typically, a 1:1 relationship exists between a physical computer and the software that it runs. This relationship leaves most computers vastly underused, leaving between only 5–10 percent of physical server capacity in use. The cost of the space and power required to house, run and keep these systems cool can be expensive. Provisioning physical servers is a time consuming process. In nonvirtualized environments time must be allotted to procure new hardware, place it in the datacenter, install an operating system, patch the operating system and install and configure the required applications can take weeks. This process also includes a myriad of other tasks to integrate the system into the infrastructure. For example, configuring firewall rules, enabling switch ports and provisioning storage.
Virtual Infrastructure
Virtualization enables you to run more workloads on a single server by consolidating the environment so that your applications run on virtual machines. Converting to a virtualized datacenter reduces the required datacenter square footage, rack space, power, cooling, cabling, storage and network components by reducing the sheer number of physical machines. The reduction of physical machines can be realized by converting physical machines to virtual machines and consolidating the converted machines onto a single host. Using virtualization technology also changes the way servers are provisioned. You do not need to wait for the hardware to be procured or cabling to be installed. Virtual machine provisioning is performed using an intuitive graphical user interface. In contrast to the long process of deploying physical servers, deploying virtual machines can be deployed in a matter of minutes.
Physical and Virtual Architecture
Virtualization provides a solution to many of the problems that are faced by IT staff. Virtualization is a technology that decouples physical hardware from a computer operating system. Virtualization allows you to consolidate and run multiple workloads as virtual machines on a single computer. A virtual machine is a computer that is created by software that, like a physical computer, runs an operating system and applications. Each virtual machine contains its own virtual hardware, including a virtual CPU, memory, hard disk, and network interface card, which look like physical hardware to the operating systems and applications. The graphics shown in the slide illustrate the differences between a virtualized and a nonvirtualized host. In traditional architectures, the operating system interacts directly with the installed hardware. It schedules processes to run, allocates memory to applications, sends and receives data on network interfaces and reads from and writes to attached storage devices. In comparison, a virtualized host interacts with installed hardware through a thin layer of software called the virtualization layer or hypervisor. The hypervisor provides physical hardware resources dynamically to virtual machines as needed to support the operation of the virtual machines. The hypervisor allows virtual machines to operate with a degree of independence from the underlying physical hardware. For example, a virtual machine can be moved from one physical host to another. Also, its virtual disks can be moved from one type of storage to another without affecting the functioning of the virtual machine.
Why Use Virtual Machines?
In a physical machine, the operating system (Windows, UNIX, Linux, and so on) is installed directly on the hardware. The operating system requires specific device drivers to support specific hardware. If the computer is upgraded with new hardware, new device drivers are required. In cases where applications interface directly with hardware drivers an upgrade to the hardware, drivers, or both can have significant repercussions if incompatibilities exist. This puts the onus of testing hardware upgrades against a wide variety of application suites and operating systems on the hands-on technical support personnel. Virtualizing these systems saves on this cost because virtual machines are 100 percent software. The virtual machine is a set of files. A virtual machine uses standardized virtual device drivers. The hardware can be upgraded without change to the virtual machine.
Multiple virtual machines are isolated from one another. You can have a database server and an email server running on the same physical computer. The isolation between the virtual machines means that software-dependency conflicts are not a problem.
Even a user with system administrator privileges on a virtual machine’s guest operating system cannot breach this layer of isolation to access another virtual machine without privileges explicitly granted by the VMware ESXi™ system administrator. As a result of virtual machine isolation, if a guest operating system running in a virtual machine fails, other virtual machines on the same host continue to run. The guest operating system failure has no effect on:
• The ability of users to access the other virtual machines
• The ability of the operational virtual machines to access the resources that they need
• The performance of the other virtual machines
Virtual machines allow you to consolidate your physical servers and make more efficient use of your hardware. Because a virtual machine is a set of files, features not available or not as efficient on physical architectures are now available to you. For example:
• Rapid and consistent provisioning
• Disaster recovery and business continuity options. With virtual machines you can use live igration, fault tolerance, high availability, improve disaster recovery scenarios and so on that increase uptime and reduce recovery time in the event of failures
• Multitenancy enables the ability to mix virtual machines into specialized configurations such as a DMZ.
• Security options available that are not in the physical infrastructure such as using VMware® vShield™ products to secure your perimeter and provide endpoint solutions. With virtual machines, you can support legacy applications and operating systems on newer hardware when maintenance contracts on the existing hardware expire.
Resource Sharing
A key concept to understanding virtualization is the notion that physical resources are shared. Virtualization lets you run multiple virtual machines on a single physical machine, with each virtual machine sharing the resources of that one physical computer across multiple environments. Virtual machines share access to CPUs and are scheduled to run by the hypervisor. In addition, virtual machines are assigned their own region of memory to use and share access to the physical network cards and disk controllers. Different virtual machines can run different operating systems and applications on the same physical computer.
When multiple virtual machines run on an ESXi host, each virtual machine is allocated a portion of the physical resources. The hypervisor schedules virtual machines, much like a traditional operating system allocates memory for and schedules applications to run on various CPUs. Virtual machines, like applications, use network and disk bandwidth. However, virtual machines are managed with elaborate control mechanisms to manage how much access is available for each virtual machine. With the default resource allocation settings, all virtual machines associated with the same ESXi host receive an equal share of available resources.
CPU Virtualization
CPU virtualization emphasizes performance and runs directly on the available CPUs whenever possible. The underlying physical resources are used whenever possible and the virtualization layer runs instructions only when needed to make virtual machines operate as if they were running directly on a physical machine.
CPU virtualization is not emulation. Do not confuse emulation with virtualization. The difference is that with emulation all operations are run in software by a software emulator. A software emulator allows programs to run on a computer system other than the one for which they were originally written. The emulator does this by emulating, or reproducing, the original computer’s behavior by accepting the same data or inputs and achieving the same results. Emulation provides portability and runs software designed for one platform across several platforms, but usually performance is negatively affected.
When many virtual machines are running on an ESXi host, those virtual machines might compete for CPU resources. When CPU contention occurs, the ESXi host time-slices the physical processors across all virtual machines so each virtual machine runs as if it has a specified number of virtual processors.
Physical and Virtualized Host Memory Usage
In a nonvirtual environment, the operating system assumes it owns all physical memory in the system. When an application starts it uses the interfaces provided by the operating system to allocate or release virtual memory pages during the execution. Virtual memory is a well-known technique used in most general-purpose operating systems, and almost all modern processors have hardware to support it. Virtual memory creates a uniform virtual address space for applications and allows the operating system and hardware to handle the address translation between the virtual address space and the physical address space. This technique adapts the execution environment to support large address spaces, process protection, file mapping, and swapping in modern computer systems.
In a virtualized environment, the VMware® virtualization layer creates a contiguous addressable memory space for the virtual machine when it is started. The memory space allocated is configured when the virtual machine is created and has the same properties as the virtual address space. This configuration allows the hypervisor to run multiple virtual machines simultaneously while protecting the memory of each virtual machine from being accessed by others.
Physical and Virtual Networking
The key virtual networking components in virtual architecture are virtual Ethernet adapters and virtual switches. A virtual machine can be configured with one or more virtual Ethernet adapters. Virtual switches allow virtual machines on the same ESXi host to communicate with each other using the same protocols that would be used over physical switches, without the need for additional hardware. Virtual switches also support VLANs that are compatible with standard VLAN implementations from other vendors, such as Cisco.
VMware technology lets you link local virtual machines to each other and to the external network through a virtual switch. A virtual switch, like a physical Ethernet switch, forwards frames at the data link layer. An ESXi host might contain multiple virtual switches. The virtual switch connects to the external network through outbound Ethernet adapters. The virtual switch is capable of binding multiple vmnics together, in a manner much like network interface card (NIC) teaming on a traditional server, offering greater availability and bandwidth to the virtual machines using the virtual switch.
Virtual switches are similar to modern physical Ethernet switches in many ways. Like a physical switch each virtual switch is isolated and has its own forwarding table, so every destination the switch looks up can match only ports on the same virtual switch where the frame originated. This feature improves security, making it difficult for hackers to break virtual switch isolation. Virtual switches also support VLAN segmentation at the port level, so that each port can be configured as an access or trunk port, providing access to either single or multiple VLANs.
However, unlike physical switches, virtual switches do not require a spanning tree protocol, because a single-tier networking topology is enforced. Multiple virtual switches cannot be interconnected and network traffic cannot flow directly from one virtual switch to another virtual switch on the same host. Virtual switches provide all the ports that you need in one switch. Virtual switches need not be cascaded because virtual switches do not share physical Ethernet adapters and leaks between virtual switches do not occur.
Physical File Systems and VMware vSphere VMFS
Conventional file systems allow only one server to have read-write access to the same file at a given time. By contrast, VMware vSphere® VMFS enables a distributed storage architecture that allows multiple ESXi hosts concurrent read and write access to the same shared storage resources. VMFS is designed, constructed and optimized for a virtualized environment. VMFS is a high-performance cluster file system designed for virtual machines. VMFS uses distributed journaling of its file system meta data changes to allow fast and resilient recovery in the event of a hardware failure. VMFS increases resource use by providing multiple virtual machines with shared access to a consolidated pool of clustered storage. VMFS is also the foundation for distributed infrastructure services such as live migration of virtual machines and virtual machine files, dynamically balance workloads across available compute resources, automated restart of virtual machines and fault tolerance.
VMFS provides an interface to storage resources so that several storage protocols (Fibre Channel, Fibre Channel over Ethernet, iSCSI and NAS) can be used to access datastores on which virtual machines can reside. Dynamic growth of VMFS datastores through aggregation of storage resources and dynamic expansion of a VMFS datastore gives you the ability to increase a shared storage resource pool with no downtime. In addition, you have a means for mounting a point in time copy of a datastore.
However, no other clustered file system provides the capabilities of VMFS. Its distributed locking methods forge the link between the virtual machine and the underlying storage resources in a manner that no other clustered file system can equal. The unique capabilities of VMFS allow virtual machines to join a cluster seamlessly, with no management overhead.
Encapsulation
VMFS stores all the files that make up the virtual machine into a single directory. VMFS provides encapsulation of the entire virtual machine so that it can easily become part of a business continuity or disaster recovery solution.
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