3.4. Virtualization

Converting a physical server running either Red Hat Enterprise Linux 4 or Red Hat Enterprise Linux 5 which has its file system root on an MD device is not supported. Converting such a guest results in a guest which fails to boot. Note that conversion of a Red Hat Enterprise Linux 6 server which has its root on an MD device is supported.

When converting a physical host with a multipath storage, Virt-P2V presents all available paths for conversion. Only a single path must be selected. This must be a currently active path.

The following parameter has been deprecated in the /etc/vdsm/vdsm.conf file:

[irs]
nfs_mount_options = soft,nosharecache,vers=3

This parameter will continue to be supported in versions 3.x, but will be removed in version 4.0 of NFS. Customers using this parameter should upgrade their domains to V2 and greater and set the parameters from the GUI.

When adding a bond to an existing network, its world-visible MAC address may change. If the DHCP server is not aware that the new MAC address belongs to the same host as the old one, it may assign the host a different IP address, that is unknown to the DNS server nor to Red Hat Enterprise Virtualization Manager. As a result, Red Hat Enterprise Virtualization Manager VDSM connectivity is broken.

To work around this issue, configure your DHCP server to assign the same IP for all the MAC addresses of slave NICs. Alternatively, when editing a management network, do not check connectivity, and make sure that Red Hat Enterprise Virtualization Manager / DNS use the newly-assigned IP address for the node.

Vdsm uses cgroups if they are available on the host. If the cgconfig service is turned off, turn it on with the chkconfig cgconfig on command and reboot. If you prefer not to reboot your system, restarting the libvirt service and vdsm should be sufficient.

Upgrades from Beta to the GA version will result in an incorrect partitioning of the host. The GA version must be installed clean. UEFI machines must be set to legacy boot options for RHEV-H to boot successfully after installation.

When a system boots from SAN, it starts the libvirtd service, which enables IP forwarding. The service causes a driver reset on both Ethernet ports which causes a loss of all paths to an OS disk. Under this condition, the system cannot load firmware files from the OS disk to initialize Ethernet ports, eventually never recovers paths to the OS disk, and fails to boot from SAN. To work around this issue add the bnx2x.disable_tpa=1 option to the kernel command line of the GRUB menu, or do not install virtualization related software and manually enable IP forwarding when needed.

If the /root/.ssh/ directory is missing from a host when it is added to a Red Hat Enterprise Virtualization Manager data center, the directory is created with a wrong SELinux context, and SSH'ing into the host is denied. To work around this issue, manually create the /root/.ssh directory with the correct SELinux context:

~]# mkdir /root/.ssh
~]# chmod 0700 /root/.ssh
~]# restorecon /root/.ssh

VDSM now configures libvirt so that connection to its local read-write UNIX domain socket is password-protected by SASL. The intention is to protect virtual machines from human errors of local host administrators. All operations that may change the state of virtual machines on a Red Hat Enterprise Virtualization-controlled host must be performed from Red Hat Enterprise Virtualization Manager.

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 the /etc/libvirt/qemu.conf file, set the relaxed_acs_check = 1 parameter, and restart libvirtd (service libvirtd restart). 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 the 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 to the network. To work around this issue, use the service libvirt reload command to restore libvirt's additional iptables rules.

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.

Installation of Windows 7 Ultimate x86 (32-bit) Service Pack 1 on a guest with more than 4GB of RAM and more than one CPU from a DVD medium often crashes during the final steps of the installation process due to a system hang. To work around this issue, use the Windows Update utility to install the Service Pack.

A dual function Intel 82576 Gigabit Ethernet Controller 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.

The virt-v2v utility is able to convert guests running on an ESX server. However, 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 the underlying storage are on different datastores, virt-v2v will report a 404 error while trying to retrieve the storage.

The VMware Tools application 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 start-up, and a "Stop Error" (also known as a BSOD) when shutting down the guest. To work around this issue, uninstall VMware Tools on Microsoft Windows guests prior to conversion.