Paravirtualized Machine

A Paravirtualized Machine is a virtualized machine that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware.

• Context:
  • Advantages:
    1. It can achieve complete isolation and secure isolation.
    2. It can run a full unmodified OS, excluding bootloader + kernel
    3. It can compile and load your own kernel modules.
    4. It can be highly scalable, low overheads.
    5. It can easily reload the OS (with precreated templates)
    6. It can directly allocate RAM + HDD (not oversold and cannot be used by other VPS)
    7. It can be easily upgraded/downgraded or migrated to another host machine
  • Disadvantages:
    1. It can only support Linux.
    2. Limited to only the precreated OS templates
    3. It can't modify the OS options during install
    4. It can't compile and install a custom kernel unless using Pygrub
    5. Fixed two filesystem layout with two partitions, one for hdd one for swap
• See: HVM Virtualized.

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References

2013

• http://en.wikipedia.org/wiki/Paravirtualization
  • In computing, paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware.

    The intent of the modified interface is to reduce the portion of the guest's execution time spent performing operations which are substantially more difficult to run in a virtual environment compared to a non-virtualized environment. The paravirtualization provides specially defined 'hooks' to allow the guest(s) and host to request and acknowledge these tasks, which would otherwise be executed in the virtual domain (where execution performance is worse). A successful paravirtualized platform may allow the virtual machine monitor (VMM) to be simpler (by relocating execution of critical tasks from the virtual domain to the host domain), and/or reduce the overall performance degradation of machine-execution inside the virtual-guest.

    Paravirtualization requires the guest operating system to be explicitly ported for the para-API — a conventional OS distribution that is not paravirtualization-aware cannot be run on top of a paravirtualizing VMM. However, even in cases where the operating system cannot be modified, components may be available that enable many of the significant performance advantages of paravirtualization. For example, the Xen Windows GPLPV project provides a kit of paravirtualization-aware device drivers, licensed under the terms of the GPL, that are intended to be installed into a Microsoft Windows virtual-guest running on the Xen hypervisor.

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