10.5. Read Only Disks in Red Hat Virtualization
Some applications require administrators to share data with read-only rights. You can do this when creating or editing a disk attached to a virtual machine via the Disks tab in the details view of the virtual machine and selecting the Read Only check box. That way, a single disk can be read by multiple cluster-aware guests, while an administrator maintains writing privileges.
You cannot change the read-only status of a disk while the virtual machine is running.
Mounting a journaled file system requires read-write access. Using the Read Only option is not appropriate for virtual disks that contain such file systems (e.g. EXT3, EXT4, or XFS).