2.4. Virtualization

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.

Booting Red Hat Enterprise Linux 6.2 as an HVM guest with more than one vCPU on machines that support SMEP and using Red Hat Enterprise Linux 5.7 and earlier Xen Hypervisors fails. To work around this issue, boot the guest with the nosmep kernel command line option.

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 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.

In Red Hat Enterprise Linux 6.2, the default virt-v2v configuration is split into two files: /etc/virt-v2v.conf and /var/lib/virt-v2v/virt-v2v.db. The former now contains only local customizations, whereas the latter contains generic configuration which is not intended to be customized. Prior to Red Hat Enterprise Linux 6.2, virt-v2v's -f flag defaulted to /etc/virt-v2v.conf. In Red Hat Enterprise Linux 6.2, it now defaults to both /etc/virt-v2v.conf and /var/lib/virt-v2v/virt-v2v.db. Data from both of these files is required during conversion.

This change has no impact for most users. If a machine is upgraded from Red Hat Enterprise Linux 6.1 to Red Hat Enterprise Linux 6.2, the existing combined /etc/virt-v2v.conf will not be updated. If a user explicitly specifies -f /etc/virt-v2v.conf on the command line, the behavior will be identical to the one prior to update. If the user does not specify the -f command line option, the configuration will use both /etc/virt-v2v.conf and /var/lib/virt-v2v/virt-v2v.db, with the former taking precedence.

However, a freshly-installed Red Hat Enterprise Linux 6.2 machine with a default configuration no longer has all required data in /etc/virt-v2v.conf. If the user explicitly specifies -f /etc/virt-v2v.conf on the command line, virt-v2v will not be able to enable virtio support for any guests.

To work around this issue, do use the -f command line option, as this defaults to using both configuration files. If the -f command line option is used, it must be specified twice: first for /etc/virt-v2v.conf and second for /var/lib/virt-v2v/virt-v2v.conf.

If the virt-v2v command line cannot be altered, the /etc/virt-v2v.conf file must contain a combined configuration file. This can be copied from a Red Hat Enterprise Linux 6.1 system, or created by copying all configuration elements from /var/lib/virt-v2v/virt-v2v.db to /etc/virt-v2v.conf.

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.

Sound recording only works when there is no application accessing the recording device at the client start-up.