Chapter 2. Restrictions and Support
The following items must be considered before 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.
Support for para-virtualized drivers is available for the following operating systems and versions:
Red Hat Enterprise Linux 5.1
Red Hat Enterprise Linux 4 Update 6
Red Hat Enterprise Linux 3 Update 9
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 |
The table above is for guest operating systems. Hardware versions X,Y and Z on Red Hat Enterprise Linux 5.1 and above are the supported choice for the host.
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 will look something like 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.
The para-virtualized device driver needs to be installed after the successful installation of the guest operating system.
A guest cannot be booted from a device that uses the para-virtualized block device drivers. Specifically, the disk that contains the Master Boot Record (MBR), the disk that contains the bootloader (GRUB), and the disk that contains the kernel initrd images (i.e., the disk that contains the /boot directory or partition) cannot use the para-virtualized block device drivers. (This is because GRUB does not how to access para-virtualized block devices.)
If you are creating (installing) a new guest system, in order to gain maximal benefit from the para-virtualized block device drivers, you should create the guest with at least two disks.
Specifically, use the first disk to install the MBR and the bootloader (GRUB), and to contain the /boot partition. (This disk can be very small, as it only needs to have enough capacity to hold the /boot partition.
Use the second disk and any additional disks for all other partitions (e.g. /, /usr) or logical volumes.
Using this installation method, when the para-virtualized block device drivers are later installed (after completing the install of the guest), only booting the guest and accessing the /boot partition will use the non-para-virtualized block device drivers.
After you installed the para-virtualized drivers in a guest operating system you should only use the xm command to start the guests. If xm is not used the network interfaces (for example, eth1) will not get connected correctly during boot. This problem is known and the Bugzilla number is 300531. A fix is in progress. The bug connects the network interface to qemu-dm and subsequently limits the performance dramatically.
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 |
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 | i386 |
| athlon-SMP | i386 |
| x86_64 | x86_64 |
| x86_64-SMP | x86_64 |