OS Virtualization Principles

Principles

• Run multiple instances of OSes simultaneously
• Multitasking at the OS level
• Garantee isolation between OSes
• Provide controlled resources sharing

Applications of OS Virtualization

Wide range of use cases:

• Server consolidation
• Colocation of services
• Security, isolation, maintainance
• Regression tests
• ...

Virtual Machines and Hardware

Ideally virtualization is transparent to guest OSes

• Common principle in mainframe design
• Nearly impossible with i386 design
• Running unmodified i386 OS guests is horribly tricky
• Those tricks kills performances in some scenarii

4 ways to run i386 OS guests

How to circumvent the lack of virtualization support

• Emulate an ideal processor: QEmu, emulators
• Rewrite the code transparently: VMWare
• Recompile the OS for virtualization: Xen, paravirtualization
• Fix the CPU: Intel VT-X, AMD Pacifica

Paravirtualization and Xen

Xen comes from the University of Cambridge

Do not hide the virtualization from the guest OSes

• Port the OS to work with Xen
• Reuse the OS drivers, but monitor hardware access
• Linux, NetBSD. FreeBSD, OpenSolaris and Plan9 worked on.

Xen's performances

Borrowed from their paper at SOSP in 2003

Xen's performances II

Borrowed from 2005 presentation at OLS

Xen's performances III

Borrowed from 2005 presentation at OLS

Xen for Linux

Xen is been integrated in Linux upstream ... slowly

• this is a separate sub architecture of i386/x86_64/ia64
• Xen runs as the hypervisor, linux runs in ring 1 or 3
• kernel instances call the hypervisor for resources
• the hypervisor uses linux first domain for the drivers

Xen Architecture

Current state

Xen is still a work in progress:

• Not integrated upstream, kernel API design ongoing
• Large changes happen, incompatibles ones
• Basic tools exists
• Integration in OS tools has started

Features

Core functionalities are here

• Create, Reboot, Shutdown, Destroy
• Suspend, Resume in memory
• Save, Restore from disk images
• Device support: Disks, Networking, Console
• Migration of domains [*]

[*] assuming conditions are met

Xen's migration data

Borrowed from this year presentation at OLS

Still a work in progress

Virtualization in general is moving fast

• Many virtualization solutions appears
• Hardware support progresses (CPU and devices)
• Storage specific solutions, snapshots
• Consolidation of APIs
• High level tools design (dynamic placement)

Red Hat involvement

Stabilize, stabilize, stabilize ...

• Integration in Linux kernel
• Regression testing, security audit, bug fixes
• Isolation layer: libvirt
• Management tools: virt-manager
• Integration in Fedora Core and RHEL management tools

Useful Links

Fedora Xen Kickstart

Fedora Virtualization

Xen FAQ Wiki

Cambridge Lab. Xen page

XenSource

Questions ?

Come see the demo