Chapter 13. Virtualization

It is now possible to use the Red Hat Enterprise Virtualization Hypervisor to access virtual machines directly using virt-viewer.

Using the remote-viewer tool to connect to an ovirt:// URI now displays a menu that allows the user to change the CD image inserted in the virtual machine (VM). This makes it possible to change the inserted CD while the VM is running without the need to use Red Hat Enterprise Virtualization or the oVirt portal.

The rest package has been added to this release as a dependency of the libgovirt package. The libgovirt package allows the remote-viewer tool to connect to virtual machines managed by oVirt and Red Hat Enterprise Virtualization.

The qemu-img tool now includes the fallocate() system call to improve performance of the preallocation=full option. To use the fallocate() system call, specify preallocation=falloc when creating a qcow2 image with qemu-img. The preallocation operation runs significantly faster with preallocation=falloc specified, thus shortening the time necessary to prepare a new guest.

KVM virtual machines use the kvm-clock utility as the time source that synchronizes the virtual machine system time with the host system time after resuming from suspend mode. Previously, in some cases when a virtual machine running on a Red Hat Enterprise Linux 6 host was suspended to disk and then restored, the virtual machine's system time did not correctly synchronize with the host system time. With this update, kvm-clock has been modified to reliably synchronize with the system time on the host.

Support has been added for qemu-kvm trace events during the virtual machine system shutdown process, which allows users to get detailed diagnostics about a guest system's shutdown requests issued by the virsh shutdown command or by the virt-manager application. This provides users with enhanced capabilities for isolating and debugging KVM guest problems during shutdown.

With this update, qemu-kvm supports the cache=directsync option in the host file, which enables the use of the directsync cache mode on virtual disks. When cache=directsync is set on the virtual disk (configured in the guest XML or the virt-manager application), write operations on the virtual machine are only completed when data is safely on the disk. This increases data security during file transactions between virtual machines, and also improves performance by allowing I/O from the guest to bypass the host page cache.

Support for encrypted passwords has been added to the virt-who service. Previously, the passwords for external services were stored in the configuration file as plain text, which exposed the password to any user with read privileges. This update introduces the virt-who-password utility, which allows encrypted passwords to be stored in the virt-who configuration file. With this change, all users who open the virt-who configuration file will see the passwords as encrypted. The encrypted passwords can be decrypted by the root user.

The virt-who service can now report the association between host physical machines and guest virtual machines when the hypervisor is offline, and thus no longer requires connection to the hypervisor to perform this operation. When the virt-who service cannot connect to the hypervisor, due to security policies, for example, users can now obtain information about the host-guest mapping file by using the virt-who --print command, which displays the information saved in the mapping file, and sends it to the Subscription Manager.

With this update, the virt-who service introduces a filtering mechanism for the Subscription Manager reports. As a result, users can now choose which hosts virt-who should display according to the specified parameters. For example, hosts that do not run any Red Hat Enterprise Linux guests, or hosts that run guests of a specified version of Red Hat Enterprise Linux.

With this update, the virt-who service introduces a filtering mechanism for the Subscription Manager reports. As a result, users can now choose which clusters virt-who should display according to the specified parameters. For example, hosts that do not run any Red Hat Enterprise Linux guests, or hosts that run guests of a specified version of Red Hat Enterprise Linux.

In cases where it is not necessary to report all the hypervisors, such as those that do not have any associated Red Hat Enterprise Linux guests, virt-who is now capable of filtering out the specified hypervisors.