13.2. Para-virtualization Restrictions and Support

13.2. Para-virtualization Restrictions and Support

This section outlines support restrictions and requirements for using para-virtualized drivers on Red Hat Enterprise Linux. What we support and the restrictions put upon support can be found in the sections below.

Supported Guest Operating Systems

Support for para-virtualized drivers is available for the following operating systems and versions:

You are supported for running a 32 bit guest operating system with para-virtualized drivers on 64 bit Red Hat Enterprise Linux 5 Virtualization.

The table below indicates the kernel variants supported with the para-virtualized drivers. You can use the command shown below to identify the exact kernel revision currently installed on your host. Compare the output against the table to determine if it is supported.

# rpm -q --queryformat '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH}\n' kernel

The Red Hat Enterprise Linux 5 i686 and x86_64 kernel variants include Symmetric Multiprocessing(SMP), no separate SMP kernel RPM is required.

Take note of processor specific kernel requirements for Red Hat Enterprise Linux 3 Guests in the table below.

Kernel Architecture Red Hat Enterprise Linux 3 Red Hat Enterprise Linux 4 Red Hat Enterprise Linux 5
athlon Supported(AMD)    
athlon-SMP Supported(AMD)    
i32e Supported(Intel)    
i686 Supported(Intel) Supported Supported
i686-PAE Supported
i686-SMP Supported(Intel) Supported  
i686-HUGEMEM Supported(Intel) Supported  
x86_64 Supported(AMD) Supported Supported
x86_64-SMP Supported(AMD) Supported  
x86_64-LARGESMP Supported  
Itanium (IA64) Supported
Table 13.1. Supported kernel architectures for para-virtualized drivers

Note

The table above is for guest operating systems. AMD and Intel processors are supported for the Red Hat Enterprise Linux 5.1 host.

Take note

Write the output of the command below down or remember it. This is the value that determines which packages and modules you need to download.

# rpm -q --queryformat '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH}\n' kernel

Your output should appear similar to this:

kernel-PAE-2.6.18-53.1.4.el5.i686

The name of the kernel is PAE(Physical Address Extension), kernel version is 2.6.18, the release is 53.1.4.el5 and the architecture is i686. The kernel rpm should always be in the format kernel-name-version-release.arch.rpm.

Important Restrictions

Para-virtualized device drivers can be installed after successfully installing a guest operating system. You will need a functioning host and guest before you can install these drivers.

Para-virtualized block devices and GRUB

GRUB can not presently, access para-virtualized block devices. Therefore, a guest can not be booted from a device that uses the para-virtualized block device drivers. Specifically, the disk that contains the Master Boot Record(MBR), a disk containing a boot loader (GRUB), or a disk that contains the kernel initrd images. That is, any disk which contains the /boot directory or partition can not use the para-virtualized block device drivers.

After installing the para-virtualized drivers on a guest operating system you should only use the xm command or virsh to start the guests. If xm is not used the network interfaces (for example, eth1 and so on) will not be connected correctly during boot. This problem is known and the Bugzilla number is 300531 and a bug fix is in progress. The bug connects the network interface to qemu-dm and subsequently limits the performance dramatically.

Red Hat Enterprise Linux 3 kernel variant architecture dependencies

For Red Hat Enterprise Linux 3 based guest operating systems you must use the processor specific kernel and para-virtualized driver RPMs as seen in the tables below. If you fail to install the matching para-virtualized driver package loading of the xen-pci-platform module will fail.

The table below shows which host kernel is required to run a Red Hat Enterprise Linux 3 guest on if the guest was compiled for an Intel processor.

Guest kernel type Required host kernel type
ia32e (UP and SMP) x86_64
i686 i686
i686-SMP i686
i686-HUGEMEM i686
Table 13.2. Required host kernel architecture for guests using para-virtualized drivers on Red Hat Enterprise Linux 3 for Intel processors

The table below shows which host kernel is required to run a Red Hat Enterprise Linux 3 guest on if the guest was compiled for an AMD processor.

Guest kernel type Required host kernel type
athlon i686
athlon-SMP i686
x86_64 x86_64
x86_64-SMP x86_64
Table 13.3. Required host kernel architectures for guests using para-virtualized drivers on Red Hat Enterprise Linux 3 for AMD processors

Note

After installing the para-virtualized drivers on a guest operating system you should only use the xm command or the virsh command to start the guests. If xmor virsh are not used the network interfaces(for example, eth1) will not be correctly connected during boot. This problem is known and the Bugzilla number is 300531. The bug connects the network interface to qemu-dm and subsequently limits the performance dramatically. A bug fix is presently in development and will be released via RHN.


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