Virtualization Technologies - P. Riteau

7/31/2019 Virtualization Technologies - P. Riteau

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What is virtualization?System-level Virtualization

Advanced Virtualization MechanismsSummary

An Overview of Virtualization Technologies

Pierre Riteau

University of Rennes 1, IRISAINRIA Rennes - Bretagne Atlantique

June 29, 2011 / Contrail Summer School 2011

Pierre Riteau An Overview of Virtualization Technologies 1/44
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Introduction

Virtualization

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Outline

1 What is virtualization?Concept of VirtualizationDifferent Types of Virtualization

2 System-level Virtualization

3 Advanced Virtualization Mechanisms

Live MigrationMemory ManagementSnapshots

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Concept of VirtualizationDifferent Types of Virtualization

Outline






Wh i i li i ?


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Virtualization vs Abstraction

Virtualization is abstraction.


Wh t i i t li ti ?
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Virtualization vs Abstraction

Virtualization is abstraction.


What is virtualization?


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Abstraction

Abstraction Offer a simplified interface

Computing systems organized as layers ofabstraction each layer helps to simplify the system

Example of abstractions

A file is an abstraction of disk storage

A TCP stream is an abstraction of network packets. . . which are abstraction of electrical signals




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Virtualization

Virtualization Offer a different interface

Virtualized interface is not necessarily simplerCan be applied to many types of resources

Compute (CPU)Storage (disk)Network

Concept of virtual machine




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Different Types of Virtualization

System-level virtualizationProcess-level Virtualization

OS Virtualization




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System-level Virtualization

Emulates a computer similar to a real physical one

With CPU(s), memory, disk(s), network interface(s), etc.

The virtual machine runs a full OS

Full Virtualization vs Paravirtualization

Examples: VMware, Xen, KVM


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System-level VirtualizationAdvanced Virtualization Mechanisms

Summary



Physical node

Kernel Kernel Kernel

Userland Userland Userland




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Summary


Process-level Virtualization

The virtual machine runs one application (one process)

Application has to be written specifically for the VM

Usually implemented on top of an operating systemExample: Java Virtual Machine

Advantage

Application is portable among all platforms supporting the VM JVM on Windows, Linux, OS X, PDAs, phones . . .

Disadvantage

Legacy applications have to be rewritten for the VM




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Summary


Process-level Virtualization

Physical node

OS

utilities

Kernel

ProcessVM

App

ProcessVM

App


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Summary


OS Virtualization

The virtual machine runs a set of userland processes

Userland domains are separated

Kernel is the same for all userland domains

Example: OpenVZ, Solaris zones, FreeBSD jails


What is virtualization?S l l Vi li i C f Vi li i
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Summary


OS Virtualization

Physical node

Userland Userland

Kernel

Userland


What is virtualization?S st l l Vi t li ti
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Summary

Outline






What is virtualization?System level Virtualization
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Summary


Virtual machines are managed by another software layer

Hypervisor / Virtual Machine Manager (VMM)Can be of two different types

Type 1: native, runs directly on hardwareType 2: hosted on top of another operating system Host OS


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Summary

Type 1 Hypervisor

Hardware

Type 1 Hypervisor

Privilegeddomain Guest domains

Privileged

OS

GuestOS

GuestOS

Userland Userland Userland




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System level VirtualizationAdvanced Virtualization Mechanisms

Summary

Type 2 Hypervisor

Hardware

Host OS

Userland

Guest domains

GuestOS

GuestOS

Userland Userland

Type 2 Hypervisor


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System level VirtualizationAdvanced Virtualization Mechanisms

Summary

Full Virtualization

Full Virtualization Run an OS without modification

Initiated by IBM in 1967 with the CP-40 system

Run natively most processor instructions

Trap and emulate privileged instructions (I/O access, systemCPU registers, . . . )

Example

Virtual machine application runs a ADD instruction

runs directly on processor without hypervisor being involvedVirtual machine kernel reads the current system level trapped by hypervisor and emulated to show a fake value




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yAdvanced Virtualization Mechanisms

Summary

Paravirtualization

Modify the guest OS to improve performance

Make the guest OS aware that it is being virtualized

Modify privileged instructions in the guest OS to avoid trapsReplace by an interaction between the guest OS and thehypervisor interface

Examples

Disco (Stanford University, 1997)Xen (University of Cambridge, 2003)




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Paravirtualized drivers

Keep the guest OS unmodified . . .

. . . but write drivers that know the system is virtualized

Emulation of a real device simple virtual deviceExamples

virtio in KVM for Linux guestsVMware Tools for Windows/Linux guests

Used for I/O devices requiring high performance

Network I/ODisk I/O


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Problems with virtualizing the Intel x86

Classical x86 architecture is not virtualizable

Some privileged instructions dont generate traps

sensitive instructionsConcept of ring levels

Normal system

OS runs in ring 0

applications in ring 3

Virtualized settinghypervisor runs in ring 0

guest OS in ring 3



Ad d Vi li i M h i


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How to virtualize the Intel x86

Binary translation recompilation of code

hypervisor analyzes guest code and replaces itwith emulated code

Paravirtualization

Hardware support

creates ring -1 for hypervisor

guest OS can run in ring 0AMD-V & VT-x



Ad d Vi t li ti M h i

Live MigrationMemory Management
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y gSnapshots

Outline



3 Advanced Virtualization MechanismsLive MigrationMemory ManagementSnapshots



Advanced Virtualization Mechanisms



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y gSnapshots

Live Migration of Processes

Migration of processes has long been researched

Offers many advantages

Load balancingPower efficiencyTransparent infrastructure maintenance

Problems

Complex implementations required to migrate all system

resourcesResidual dependencies






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Snapshots

Live Migration of Virtual Machines

Virtual machines provide complete encapsulation ofApplicationsLibrariesOperating system

Possible to serialize the state of a VM between physical hosts

Source Host Destination Host

VM VM

Live Migration




Live MigrationMemory ManagementS
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Snapshots

Live Migration of VMs in LANs

Transfer VM state from source host to destination host

VM state

Processor state (CPU registers)Device state (hardware registers)Memory content

What about storage and network resources?

Shared storage (e.g. NFS) no migration needed

Network traffic redirected with gratuitous ARP/RARP frames




Live MigrationMemory ManagementS h


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Snapshots

Live Migration of Virtual Machines


VM VMLive Migration

Shared FS Server

VM disk

ARP/RARP frame




Live MigrationMemory ManagementS h t
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SummarySnapshots

Pre-Copy Live Migration

Traditional method used for migration of processes

Iterative process

Copy all memory content to the destination host(while the VM continues running)Do multiples iterations to copy modified memory pages duringthe previous periodWhen enough iterations have been done, stop the VM and

Copy the remaining modified memory pages

Copy the CPU and device state

Resume VM on destination host




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SummarySnapshots

Post-Copy Live Migration

Pre-copy: can present long downtime in the last phase

if the application modifies a large working setif the available bandwidth is low

Post-copy algorithmStart by copying CPU and device stateResume VM execution on the destination hostFetch memory on demand when accessed

Reduces downtime over pre-copyCan lower performance because of memory access latency






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SummarySnapshots

Trace & Replay Live Migration

Use pre-copy as the basic migration algorithm

Instead of sending modified memory pages send external

events of the VM to replay the modificationse.g., network packet received modify network card registers

Greatly reduces amount of data to send between hosts

Problem: not working for SMP VMs as CPU synchronization

would be too costly


What is virtualization?System-level VirtualizationAdvanced Virtualization Mechanisms

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SummarySnapshots

Live Migration over Wide Area Networks

Live migration between differentinfrastructures/data centers/clouds


VM VMLive Migration

Shared FS Server

VM disk

Internet

x



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SummarySnapshots

Live Migration of Storage

Need to replicate data to the destination infrastructure

Mechanism similar to pre-copy live migrationCopy the whole disk content

Iteratively synchronize changes

Examples: KVM migration, DRBD



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Summaryp

Network Support for Live Migration

Not possible to redirect traffic with ARP/RARP frames

between different IP networks

Solutions based on encapsulating traffic in a tunnel over WAN

Or Mobile IPv6 mechanisms



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Summary

Live Migration Optimizations

Objective: Minimize downtime

Means: Reduce amount of data to sendSeveral approaches

Data CompressionPage Delta TransferData Deduplication



Summary

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Summary

Data Compression

Compress memory pages sent over the network

Trivial approach: compress zerod memory pages

General approach: use regular compression (gzip)

More complicated: adaptive memory compression



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Summary

Page Delta Transfer

Memory pages are 4 KB on x86

Modify 1 byte in the page transfer 4 KBDelta transfer mechanism:

Keep copy of original pageComputer differences between original and new pageSend diff instead of full content



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Su a y

Data Deduplication

VMs can contain identical data in multiple memory pages

Deduplication retains only one unique copy of each memorypage

Duplicate detection based on fast hash algorithm + full datacomparison in case of match



Summary



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y

Memory Management

Virtualization properties

Multiplexing of several guest OS

Isolation

Consolidation: running multiple systems on one physicalhost

Multiple guest OS compete for memory of host



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Ballooning

Paravirtualized driver runs in the VM

Responds to hypervisor requests for memoryInflate/deflate its memory allocation

Memory is given back to the hypervisor Can be used by other VMs afterwards



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Page Sharing

Typical to run multiple times the OS on one host

Each OS will have its own copy of code and data from

kernellibrariesapplications

Detect identical pages in multiples VMs of the same host

Merge identical pages to reduce memory consumption

Mark shared pages as read-only to do copy on write



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Snapshots

Snapshot = save full state (memory + storage) of a VM

Allows to return to a previous state

Some scenariosWrong configuration change rollback to snapshotFailed OS update rollback to snapshot

Copy-On-Write (COW) for storing changes

Store only modifications made on writes



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Summary

Virtualization offers different interfaces (= abstration).

Concept of virtual machine as an execution platform

Different kinds of virtual machinesSystem-level virtualization allows to execute regular OS

Features offered by system-level virtualization

Live migration in LAN or WANMemory balancing/sharingSnapshots

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Virtualization Technologies - P. Riteau

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