7.1 What are Virtualization Modes or Domain Types?

Virtual machines may run in one of two main modes, paravirtualized (PVM) or hardware virtualized machine (HVM). In paravirtualized mode, the kernel of the guest operating system is recompiled to be made aware of the virtual environment. This allows the paravirtualized guest to run at near native speed, since most memory, disk and network accesses are optimized for maximum performance.

If support for hardware virtualization is available (either Intel® VT or AMD-V™), the guest operating system may run completely unmodified. This hardware virtualized machine is carefully monitored and trapped by Oracle VM Server when any instruction is executed which would violate the isolation with other guests or dom0. In the current implementation, there may be performance penalty for certain types of guest and access types, but hardware virtualization also allows many Microsoft Windows operating systems and legacy operating systems to run unmodified.

The third virtualization mode is a hardware virtualized machine with paravirtualized drivers (PVHVM). This mode is identical to a hardware virtualized machine, but with additional paravirtualized drivers installed in the guest's operating system to improve virtual machine performance.

When you create a virtual machine, you must choose the virtual machine virtualization mode, or domain type, as in the following table:

Table 7.1 Domain Types

Domain Type

Description

Hardware virtualized machine (HVM)

Hardware virtualization, or fully virtualized. An HVM guest, must be installed similar to bare metal, using an install ISO file or network installation server.

To create HVM guests, you may need to activate the hardware virtualization in the BIOS of the server on which you install the Oracle VM Server.

Hardware virtualized, with paravirtualized drivers (PVHVM)

Identical to HVM, but with additional paravirtualized drivers for improved performance of the virtual machine. See Converting to Paravirtualized Guests or Installing Paravirtualized Drivers for more information about using paravirtualized drivers. This Domain Type is used to run Microsoft Windows guest operating systems with an acceptable performance level and can also be used to run Oracle Linux and Oracle Solaris guest operating systems.

Paravirtualized (PVM)

When you create a PVM guest, you must supply a location for the mounted ISO file from which to create the virtual machine. Before you create the virtual machine using the paravirtualized method, mount the ISO file on an NFS share, or HTTP or FTP server. You supply the location of the mounted ISO file during the creation process.

For information on creating a mounted ISO file, see Section 7.2, “How is a Guest OS Installed on a Virtual Machine?”.

Due to kernel restrictions in both Oracle Linux 7 and RedHat Enterprise Linux 7, it is not possible to run these operating systems as PVM guests. Attempts to do so, generate an exception from within Oracle VM Manager to prevent this.

Oracle VM Server for SPARC (OVM/SPARC)

Since virtualization on SPARC platforms is significantly different to that achieved within x86 environments, Oracle VM distinguishes a separate virtualization mode specifically to indicate that the SPARC hypervisor is to be used. When creating a virtual machine that is to run in a server pool consisting of Oracle VM Servers for SPARC, this mode is used during configuration.


Note

If you want to create a PVHVM or PVM, make sure all disks the virtual machine is configured to use are paravirtual devices. An explanation and description of the steps to properly configure paravirtual disks is discussed in Paravirtualized Guest Disk Devices are Not Recognized in the Oracle VM Administrator's Guide.

Converting to Paravirtualized Guests or Installing Paravirtualized Drivers

For optimized performance, you can install paravirtualized drivers on hardware virtualized machines. Paravirtual drivers are optimized and improve the performance of the operating system in a virtual machine. These drivers enable high performance throughput of I/O operations in operating systems on top of the Oracle VM Server hosts.

Creating hardware virtualized machine machines may require that you install paravirtual drivers for your hardware on the guest operating system.

The Oracle Solaris 10 and Oracle Solaris 11 operating system runs as a hardware virtual machine (HVM), which requires HVM support (Intel® VT or AMD-V™) on the underlying hardware platform. By default, Oracle Solaris 10 or Oracle Solaris 11 operating system already has the required paravirtualized drivers installed as part of the operating system.

You can continue using HVM guest, but leverage the paravirtualized I/O drivers. For more information, see the Oracle Support document 757719.1 titled Comparison of Guest Virtualization Modes; HVM, PVM and PVHVM. Configuration, Mode Validation and Conversion to PVHVM on the My Oracle Support web site at:

https://support.oracle.com/epmos/faces/DocumentDisplay?id=757719.1.

Oracle recommends running with HVM or PVHVM guest types for optimum performance on current generation servers. Information on converting from PVM to HVM or PVHVM can be found in the Oracle Support document 757719.1.

To install the paravirtual drivers for Microsoft Windows operating systems (Oracle VM Paravirtual Drivers for Microsoft Windows), see Oracle VM Paravirtual Drivers for Microsoft Windows.