TDC 311

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TDC 311

• Server Virtualization

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What is Server Virtualization?

• Lets see a video

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What is Server Virtualization? (from Whatis.com)

• Server virtualization is the masking of server
  resources, including the number and identity of
  individual physical servers, processors, and OSs,
  from server users
• The server administrator uses a software
  application to divide one physical server into
  multiple isolated virtual environments
• Isolated environments aka partitions, guests,
  instances, containers, or emulations

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Is This a New Technology?

• No, mainframes and minis have been doing this for
  years
• IBM mainframes have perfected it

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Three Popular Approaches

• The virtual machine model
• The paravirtual machine model
• Virtualization at the operating system level
• Lets examine each of these

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The Virtual Machine Model

• Based on host/guest paradigm
• Each guest runs on a virtual imitation of the
  hardware layer
• Guest OS runs without modifications
• A hypervisor runs on top of the host machine
  which coordinates guest OS requests to the
  hardware resources (aka virtual machine monitor
  (VMM))
• Hypervisor validates all guest-issued CPU
  instructions and manages any executed code that
  requires additional privileges
• VMware and Microsofts Virtual Server use this
  model

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The Paravirtual Machine Model

• Also based on host/guest paradigm and uses a
  virtual machine monitor
• But here the VMM actually modifies the guest
  operating systems code
• This is called porting
• Porting supports the VMM so it can utilize
  privileged systems calls sparingly
• Xen and UML are examples of this model

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Virtualization at the OS Level

• Not based on host/guest paradigm
• Host runs a single OS kernel as its core and
  exports OS functionality to each of the guests
• Guests must use the same OS as the host, although
  different distributions of the same system are
  allowed
• This distributed architecture eliminates system
  calls between layers, which reduces CPU usage
  overhead

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Virtualization at the OS Level

• But each partition must remain strictly isolated
  from its neighbors so that a failure or security
  breach in one partition will not affect any other
  partition
• Common binaries and libraries on the same
  physical machine can be shared
• Virtuozzo and Solaris Zones use this model

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Is Virtualization For Everyone?

• No
• Good to great solution for small- to medium-scale
  server usage
• For example, you are taking a 12 GHz server and
  chopping it into 16 750 MHz servers
• But if 8 of those servers are in off-peak or idle
  mode, the remaining 8 servers will have nearly
  1.5 GHz available to themselves

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Is Virtualization For Everyone?

• You do not want your processor to exceed 50
  utilization during peak loads (simple rule of
  thumb)
• Following might be good choices for
  virtualization
• HTTP
• FTP
• DNS
• DHCP
• RADIUS
• LDAP
• File services using Fiber Channel or iSCSI
  storage
• Active Directory services

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Is Virtualization For Everyone?

• Potentially bad choices for virtualization
• Exchange Server
• Microsoft SQL
• MySQL
• Oracle
• Any logical server that requires two or more
  physical servers for operation

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Physical to Virtual Server Migration

• Any respectable virtualization solution will
  offer some kind of physical to virtual (P2V)
  migration tool
• This tool will take an existing physical server
  and make a virtual hard drive image of that
  server with the necessary modifications to the
  driver stack so that the server will boot and run
  as a virtual server
• Great way to support a disaster recovery plan