Server Virtualization Overview

This topic describes server virtualization.

• Hypervisor or VMM:

- Thin operating system between hardware and virtual machine

- Controls and manages hardware resources

- Manages virtual machines (creates, destroys, etc.)

- Runs on host (physical server) • Virtualizes hardware resources:

- CPU process time-sharing

- Memory span from physical memory

- Network - Storage Virtualized Server Hardware Hypervisor OS Application OS Application

CPU Memory Storage Network

A hypervisor, or virtual machine monitor (VMM), is server virtualization software that allows multiple operating systems to run concurrently on a host computer.

The hypervisor provides abstraction of the physical server hardware for the virtual machine. A thin operating system performs the following basic tasks:

n Control and management of physical resources by assigning them to virtual machines and monitoring resource access and usage

n Control and management of virtual machines—the hypervisor creates and maintains virtual machines and, if requested, destroys the virtual machine (if the VMM is alive)

Ideally, a hypervisor abstracts all physical server components—CPU, memory, network, and storage. CPU abstraction is achieved with CPU time-sharing between virtual machines, and memory abstraction is achieved by assigning memory span from a physical memory. A virtual server is used to enable a particular service or application, and, from the server perspective, CPU, memory, I/O, and storage resources are important.

Note When multiple virtual machines are deployed, they can oversubscribe resources. The hypervisor, therefore, must employ an intelligent mechanism to allow oversubscription without incurring performance penalties.

• Locally attached

- Prevents VM mobility

• Remotely attached

- FC/FCoE, iSCSI, or NAS

NAS Hypervisor OS AppOSApp OS AppOSApp OS App Hypervisor OS AppOSApp OS AppOSApp OS App Hypervisor OS AppOSApp OS AppOSApp OS App VM Files VM Files Hypervisor OS AppOSApp OS AppOSApp OS App VM Files VM Files iSCSI VM Files VM Files FC/FCoE VM Files VM Files

Traditionally, storage logical unit numbers (LUNs) are presented to the hypervisor and then formatted as volumes. Each volume can contain one or more VMs, which are stored as files on the volume:

n LUNs are masked and zoned to the hypervisor, not the VM.

n LUNs are formatted by the hypervisor with the correct clustered file system.

n VMs (operating system and data) are stored as files on volumes.

Virtual disks can be presented to the VMs as Small Computer Systems Interface (SCSI) LUNs using a virtual SCSI hardware adapter.

• Connects host and VMs to the network

- Extends network into servers • Virtual switch

- Uplink ports: physical NICs

- VM-facing ports: virtual NICs

Hypervisor OS App OS App OS App OS App Physical Server (Host) LAN

Physical NICs

Virtual Switch

Virtual NICs

Virtual Machines

The server virtualization solution extends the access layer into the host server with the VM networking layer. The following components are used to implement server virtualization networking:

n Physical network: Physical devices connecting hosts for resource sharing. Physical

Ethernet switches are used to manage traffic between hosts, the same as in a regular LAN environment.

n Virtual networks: Virtual devices running on the same system for resource sharing.

n Virtual Ethernet switch: Similar to a physical switch. It maintains table of connected

devices, which is used for frame forwarding. It can be connected via uplink to a physical switch via a physical network interface card (NIC). It does not provide the advanced features of a physical switch.

n Port group: Subset of ports on a virtual switch for VM connectivity.

n Physical NIC: Physical network interface card used to uplink host to the external network.

As multiple VMs are created on each physical server, virtual networks are also constructed to support the I/O needs of the VMs. These networks sit outside the boundary of standard networking controls and best practices.

Virtual networking is deployed on each host server and extends the access layer into configured physical servers—a virtual access layer. The virtual access layer does not have the same

functionality as a physical access layer, typically lacking access control list (ACL) and QoS configuration options.

• Virtual machine (VM) contains an operating system and application:

- Operating system = guest operating system

- Guest operating system does not have full control over hardware

- Applications are isolated from each other • VMs contain the following:

- vMAC address

- vIP address

- Memory, CPU, storage space

Virtual Machine

Operating System Application

A virtualized server is called a virtual machine (VM). A virtual machine is a container holding the operating system and the applications. The operating system in a VM is called the guest operating system.

A VM is defined as a representation of a physical machine by software that has its own set of virtual hardware on which an operating system and applications can be loaded. With

virtualization, each virtual machine is provided with consistent virtual hardware, regardless of the underlying physical hardware that the host server runs on. A virtualized server has the same characteristics as a physical machine:

n CPU

n Memory

n Network adapters

n Disks

All the virtual server resources are virtualized. Each VM also has its own set of parameters— for example, a virtual MAC address and virtual IP address—to allow it to communicate with the external world. Therefore, a single physical server will typically have multiple MAC addresses and IP addresses—those defined and used by the VMs that it serves.

Because a VM uses virtualized resources, the guest operating system is no longer in control of hardware—this is the privilege of the hypervisor. Underlying physical machine resources are shared between different virtual machines, each running its own operating system instance. The VM resources are defined by the server administrator, which creates a VM—defines the characteristics of a VM—the CPU speed, amount of memory, storage space, network connectivity, and so on.

VM Benefits

Using a VM provides four significant benefits:

n Hardware partitioning: Multiple virtual machines run on the same physical server at the

same time.

n VM isolation: A VM running on the same physical server cannot affect the stability of the

other VM.

n VM encapsulation: A VM is kept in a couple of files, which eases VM mobility.

n Hardware abstraction: The VM is not tied to a physical machine and can be moved

according to business or administrative demand. The load can be dynamically balanced among the physical machines.

• Hypervisor abstracts the hardware from the guest operating system and application

• Runs multiple operating systems on a single physical machine • Divides server system resources between VMs

Resource Pool Hypervisor Hypervisor Hypervisor Hypervisor OS AppOSApp OS AppOSApp OS App OS AppOSApp OS AppOSApp OS App OS AppOSApp OS AppOSApp OS App OS AppOSApp OS AppOSApp OS App

Partitioning means that a physical server (host) runs two or more operating systems with different applications installed. The VM operating system is called the guest operating system. The guest operating systems might be different—hypervisors typically support different operating systems, including Windows, Linux, Solaris, NetWare, or any other vendor-specific system. None of the guest operating systems have any knowledge of others running on top of the hypervisor on the same physical host. They share the physical resources of the physical server.

The control and abstraction of the hardware and physical resources is done by the hypervisor— a thin operating system that provides the hardware abstraction.

• Hardware-level fault and security isolation:

- VMs are not aware of presence of other VMs.

- VM failure does not affect other VMs on the same host. • Advanced server resource control:

- To preserve and control performance

A second key VM characteristic is isolation. Isolation means that VMs do not know about other VMs that might be running on the same host. They have no knowledge of any other VM. The implication of isolation is, of course, security. Not knowing about each other, the VMs do not interfere with data from the others. Isolation also prevents any specific VM failure from affecting any other VM operation.

VMs on the same or different physical servers can communicate if network configuration permits it.

To ensure proper performance for a VM, the hypervisor allows advanced resource control, where certain resources can be reserved per VM, such as when the hypervisor allocates and dedicates memory.

• Each VM has a state that can be saved to a set of known files. • VMs can be moved or copied (cloned):

- Simple move or copy file operation

OS APP OS APP OS APP OS APP OS APP OS APP OS APP OS APP

A third key VM characteristic is encapsulation—a VM is a collection of files on a host

operating system (the ESX storage space), which saves the VM state that contains the following information:

n The guest operating system and applications installed

n The VM parameters, including memory size, number of CPUs, and so on

An encapsulated VM can easily be moved or copied for backup or cloning purposes—this is just a simple move or copy operation on the host ESX system. A VM is independent of the underlying physical server, so it can be moved to and started on a different ESX server.

• Any VM can be provisioned or migrated to any other host with similar physical characteristics.

• Support for multiple operating systems:

- Windows, Linux, Solaris, NetWare

Resource Pool Hypervisor Hypervisor OS AppOSApp OS App OS AppOSApp OS App OS App OS App OS App OS App OS App Virtual Infrastructure

The fourth key characteristic is hardware abstraction. As already mentioned, this is performed by the ESX hypervisor to provide VM hardware independency.

Being hardware-independent, the VM can be migrated to another ESX server to use the physical resources of that server. Mobility also provides scalable, on-demand server provisioning, server resource pool growth, and failed server replacement.

With advanced VMware mechanisms such as Dynamic Resource Scheduler (DRS), the VM can be moved to a less-used physical server, thus dynamic load balancing is provided.

• Migrating live VMs:

- Moves VMs across physical servers without interruption

- Changes hardware resources dynamically

- Eliminates downtime and provides continuous service

- Balances workloads for computing resource optimization

Resource Pool Migration Hypervisor Hypervisor OS App OS App OS App OS App OS App OS App OS App OS App OS App OS App OS App

VM mobility is achieved with migration of live VMs (for example, VMware VMotion, Microsoft Hyper-V LiveMigration), which allows the moving of VMs across physical hosts with no interruption. During such a migration, the transactional integrity is preserved, and the VM resource requirements are dynamically shifted to the new host.

VM mobility can be used to eliminate downtime normally associated with hardware maintenance. It can also be employed to optimize server utilization by balancing virtual machine workloads across available host resources. VM mobility enables server administrators to transparently move running VMs from one physical server to another physical server across the Layer 2 network.

For example, a Cisco UCS blade needs additional memory. VM mobility could be used to migrate all running VMs off the blade, allowing the blade to be removed so that memory could be added without impact to VM applications.

• VM restart-based high availability:

- Automatic restart of VM upon host failure • VM instant switchover:

- Primary VM with secondary shadow copy VM

- Instant switchover in case of host failure

Secondary VM Primary VM Hypervisor Hypervisor OS App OS App OS App OS App OS App OS App OS App OS App OS App OS App Failed Host OS App OS App OS App OS App OS App OS App

In document Dcucd50 Sg Vol1 (Page 84-93)