Enterprise Linux Log

May 31 2007   4:14PM GMT

Xen 3.1, XenEnterprise and RHEL


Last week, XenSource released Xen 3.1 (formerly 3.0.5) to the community, offering significant new features and capabilities. There are a number of enhancements, but the most significant are:

XenAPI 1.0

Offers XML-based config files, virtual machine life-cycle management operations and secure XML-RPC. All of these will serve to significantly improve the manageability of the virtual environment, especially the secure XML-RPC piece. One of the big problems with Xen in the past has been its relatively weak remote management interface over insecure http. While you could technically perform a number of virtual machine management functions from a remote workstation with it, no one ever turned it on because it was wide open with no security features (save firewall rules, which really don’t work for this sort of thing in a dynamic environment.) This new API will enable the community to develop strong management tools for both operations and life-cycle. Look for the Fedora team to enable the “Remote Xen Host” field in virt-manager, as well as a variety of other remote management capabilities, now that it can be done safely.

Near feature parity for HVM guests

With Xen 3.0.x, Hardware Virtual Machine (HVM) guests running unmodified OSes (such as Windows) did not enjoy the same life-cycle capabilities as paravirtualized guests (such as Linux.) With the release of 3.1, Xen can now save, restore and migrate running HVM guests. In addition, memory can now be dynamically allocated to a running HVM guest. These capabilities are an absolute necessity in an agile virtualized infrastructure, and by adding them in version 3.1 Xen has matured to match VMWare in terms of enterprise readiness.

Native 64-bit and 32-bit guests on 64-bit hosts

Xen 3.1 steps out to lead the competition by being the first to enable native 64-bit guests, as well as enabling 64-bit hosts to run a mix of 32-bit and 64-bit guests. It’s now possible to run any supported operating system in 32- or 64-bit mode, including 64-bit Oracle, Microsoft Exchange 2007, etc. In addition, 32-bit guests on 64-bit hosts allows for maximum flexibility and resource utilization, as segregating 32-bit and 64-bit guests to specific hosts is no longer required. Both serve to make Xen a very robust platform for any virtualized environment.

So what does this mean for the major players in Xen virtualization?


The next release of XenEnterprise, due to be released later this summer, will include the Xen 3.1 core. This release is expected to bring missing enterprise features into the XenEnterprise product, such as live migration and life-cycle capabilities. In the current release, based on Xen 3.0.4, the migration of live virtual machines from host to host was not enabled, largely due to XenSource’s incessant reliance on their self-imposed, non-shareable “storage repository” design, whose focus on ease of use severely limits storage flexibility. Unfortunately, the situation won’t improve much with the new release, as XenSource will only offer one shared storage mechanism for running guests — NFS — which is semi-easy, but certainly less than ideal. But it will make live migration possible and XenSource currently plans to include the tools necessary to do so in their management console. Don’t get me wrong, XenEnterprise works very, very well overall, and is still an excellent choice, especially if you will be virtualizing Windows servers.

RHEL 5.1

Expect to see Xen 3.1 included in the first update to RHEL 5, due later this year. Since the Xen engine is standard in RHEL, expect to be able to take advantage of all the new features of Xen 3.1, without limitations. Red Hat engineers have also stated that they expect to continue to add features to their management tool set, including multi-host management and easy access to migration and life-cycle functions. Don’t expect paravirtualized drivers for Windows, however, as they probably won’t appear until version 5.2. Until then, Windows in RHEL 5 Xen will probably not be viable for most workloads. Also, while the management console will certainly improve, it’s not likely to match XenEnterprise’s offering just yet. On the flip side, RHEL offers far more flexibility as a general purpose operating system with tons of hardware and vendor support, which, depending on your needs, can certainly make up for a bit less ease of use.


Xen 3.1 represents the fruition of some of the last key elements missing in the Xen engine, bringing near feature parity with VMWare’s core capabilities. Look for rapid development of the tools to manage the engine in the coming months. Or, if you want to try it out now, Fedora 7 just came out — go download a copy!

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  • Is virtualization where Linux will top Windows…perhaps stealthily? — Server Virtualization Blog
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