TABLE OF CONTENTS Xen is an advanced virtualization solution that encapsulates three layers of virtualization: devices, memory, and CPU. Due to these types of virtualization, which are sophisticated and difficult to implement, you can achieve very good performance results with Xen.
In this chapter, we will discuss advanced Xen concepts like storage and networking, live migration, clustering, and backup solutions. Various solutions exist in these areas, and we will discuss the pros and cons of some of them.
In Xen, I/O is performed by Virtual Split Devices, which have a FrontEnd layer and a BackEnd layer. The idea behind this is safe and efficient hardware isolation. The BackEnd layer is part of domain 0 (dom0). It is the only layer that has direct access to the hardware devices in a default Xen installation. Note that it is possible to configure domUs with hardware access, too something called driver domains. Also note that work is done to enable domUs to access hardware devices (such as infiniband) without usage of driver domains for example, there is ongoing research about VMM-bypass for I/O access using infiniband for VM environments (see http://nowlab.cse.ohio-state.edu/publications/conf-papers/2006/usenix06.pdf). Each unprivileged domain has a FrontEnd layer of itself. Access from the FrontEnd to the BackEnd and backwards is performed by event channels and shared memory. Each domain can have up to 1024 event channels on i386 machines, and up to 4096 event channels on x86_64 machines. The FrontEnd and BackEnd share memory pages for communication, which is controlled by...
