4.3. Virtualization

Under some circumstances, installation of a Red Hat Enterprise Linux 6 virtual guest stalls after the optional testing of media. Note that this issue has only been observed with Red Hat Enterprise Linux 6 guests that utilize multiple virtualized CPUs. To work around this issue, use a media source that is known to be verified, and skip the media test, or use a single virtualized CPU during installation.

In earlier versions of Red Hat Enterprise Linux, libvirt permitted PCI devices to be insecurely assigned to guests. In Red Hat Enterprise Linux 6, assignment of insecure devices is disabled by default by libvirt. However, this may cause assignment of previously working devices to start failing. To enable the old, insecure setting, edit /etc/libvirt/qemu.conf, set "relaxed_acs_check = 1", and restart libvirtd. Note that this action will re-open possible security issues.

The balloon service on Windows 7 guests can only be started by the "Administrator" user.

Libvirt uses transient iptables rules for managing NAT or bridging to virtual machine guests. Any external command that reloads iptables state ( such as running system-config-firewall) will overwrite the entries needed by libvirt. Consequently, after running any command or tool that changes the state of iptables, guests may lose access the network. To work around this issue, use the command 'service libvirt reload' to restore libvirt's additional iptables rules.

KVM users with a mix of virtio and ata disks should verify the boot device that anaconda chooses during installation. To verify the boot device, locate the "Install Target Devices" list in the disk selection screen that follows the partitioning type screen. Verify the boot device selection, which is indicated by a selector in the left-most column of the "Install Target Devices" list.

A Windows virtual machine must be restarted after the installation of the kernel windows driver framework. If the virtual machine is not restarted it may crash when a memory balloon operation is performed.

A dual function, 82576 interface (codename: Kawela, PCI Vendor/Device ID: 8086:10c9) cannot have both physical functions (PF's) device-assigned to a Windows 2008 guest. Either physical function can be device assigned to a Windows 2008 guest (PCI function 0 or function 1), but not both.

virt-v2v is able to convert guests running on ESX server. A current limitation in virt-v2v means that if an ESX guest has a disk with a snapshot, the snapshot must be on the same datastore as the underlying disk storage. If the snapshot and underlying storage are on different datastores, virt-v2v will report a 404 error while trying to retrieve the storage.

VMware Tools on Microsoft Windows is unable to disable itself when it detects that it is no longer running on a VMware platform. Consequently, converting a Microsoft Windows guest from VMware ESX which has VMware Tools installed will result in errors. These errors usually manifest as error messages on startup, and a "Stop Error" (also known as a BSOD) when shuting down the guest. To work around this issue, uninstall VMware Tools on Microsoft Windows guests prior to conversion.