News Stay informed about the latest enterprise technology news and product updates.

Citrix XenServer 'on the clock' as hypervisor wars heat up

Citrix will add shared-nothing storage live migration to XenServer, to compete with Microsoft's Hyper-V.

Industry watchers have questioned the future of XenServer, given Citrix Systems Inc.'s support for Hyper-V and the lack of some important features. But it appears the company has no intention of giving up its share of the server virtualization market.

The XenServer and cloud business unit [at Citrix] is on the clock. They have a limited window in which to execute in the market and prove their relevance.

Chris Wolf,
vice president, Gartner Inc.

Citrix detailed its XenServer roadmap this week and plans to ship a new release of the hypervisor, code-named "Tampa," this quarter. It will include such long-awaited features as shared-nothing and storage live migration, a new direct VMware Inc. conversion tool, networking updates, and support for a new storage array through the StorageLink program.

Storage live migration -- dubbed Storage XenMotion by Citrix officials in a webinar broadcast on Wednesday, has been on many IT pros' wish lists for years, and some had expected it with the release of XenServer 6.0 last year.

The feature is a critical one for Citrix in the server virtualization market, said Bart Jacobs, owner of Belgium-based technology consulting firm BJ IT. "VMware has had it for a long time, Microsoft will have it -- if they don't have that feature, that will kill them," he said.

In 2013 Citrix will begin a schedule of two releases per year for two and a half years. Updates include a new "Windsor" architecture that will shrink XenServer's domain zero and introduce smaller, parallel domains for storage and networking I/O. The releases also will provide better security, serviceability, scalability and compatibility with technologies such as NUMA.

Perhaps the most important feature in Windsor is support for 64-bit hardware drivers within the new parallel domains. This will allow XenServer to support Flash storage devices from Fusion-io, for example, which today require a 64-bit driver.

Without 64-bit hardware driver support, customers that want solid-state storage have had to go with Hyper-V or VMware, said Eugene Alfaro, director of IT engineering services at Cornerstone Technologies LLC, an IT services firm based in San Jose, Calif.

Citrix concedes ground to Microsoft Hyper-V

Many virtualization industry watchers wondered whether Citrix would continue to develop XenServer to remain competitive, or would concede to partner Microsoft's Hyper-V 3. Channel partners and analysts say Citrix already has ceded ground in the enterprise to Hyper-V as a back end for its own XenApp and XenDesktop applications.

"What I'm seeing is a more willing acceptance of beginning to deploy Citrix applications on Hyper-V," Alfaro said. "As a consulting company, we decided six months ago that we're going to shift some of our designs towards Hyper-V."

Though Gartner Inc. named XenServer a leader in its recent Magic Quadrant report, the analyst firm stated that Citrix's strategy for competing with Microsoft remains confusing for customers and channel partners.

"It is apparent that Citrix is willing to sacrifice the server platform to Microsoft and Hyper-V to grow its desktop virtualization business," the report said. "The XenServer and cloud business unit [at Citrix] is on the clock," said Chris Wolf, Gartner research vice president. "They have a limited window in which to execute in the market and prove their relevance."

Project Windsor: Fixing the 'big, fat domain zero' problem

Tampa will be the last of what Citrix officials now call the generation-two architecture for XenServer. Shortly after its release, work will begin on generation three, codenamed Project Windsor. To prepare for the effort, Citrix has increased its Cambridge, U.K.-based engineering team by 20% in the first half of 2012, and plans to double its India-based development team in the next year.

"This [generation two] architecture is becoming increasingly difficult for us to keep going with," said Richard Sharp, senior director of XenServer engineering, during the webinar. "There's just too much stuff in domain zero."

The new architecture will make domain zero smaller and separate out such services as the network and storage back end, logging, consoles, and API into separate domains that run directly on the hypervisor. This will result in improved serviceability because domains can be restarted or upgraded without taking down the whole XenServer stack, and reduce "cascading" problems from an interconnected "big, fat domain zero," Sharp said. Separate storage and network domains will also improve I/O performance and make XenServer fundamentally more compatible with NUMA CPU architectures, he said.

Today, with NUMA, IT pros face a "horrible tradeoff," Sharp said. The vCPUs have to be pinned to some physical CPU, and "whatever you pick is going to be a compromise."

Multiple domain back ends can be pinned to different areas of a NUMA architecture so that it all works well, Sharp said.

Finally, a shrunken and split-up domain zero will help horizontal scalability. Sharp sees domain zero currently as a big apartment building, and every VM added is similar to adding on an extra floor, he said. "And the dom-zero tower sooner or later starts to wobble," he added.

Being able to replicate smaller blocks of VM/console domain/network interface card (NIC) domain/storage domain, and to scale them out will solve this problem, according to Sharp.

More Tampa release details

Storage XenMotion can be used for the same things as VMware's Storage vMotion and Microsoft's Storage Live Migration, but Citrix officials said new features will ship with the feature that are unique to XenServer, including the ability to live-migrate storage volumes between pools of storage and between storage formats, for example, from iSCSI to NFS.

A transfer and destination network can be selected during the process so that XenServer machines are unaffected by the process of storage live migration, or so that a private network can be used for data security. As many as three concurrent Storage XenMotions are possible per host. Storage XenMotion also will support the migration of VMs without shared storage.

In the first release, Storage XenMotion will not be compatible with XenServer's Workload Balancer (WLB) capability; only one snapshot associated with a VM image can be moved at a time; and PCI pass through for NICs or graphics processing units will not be supported.

Also new with the Tampa release will be XenServer Conversion Manager, designed specifically for converting VM images from VMware's vSphere 4 and 4.1 to XenServer. The software does this through a wizard-driven interface that doesn't require secondary "staging" shared storage. Officials hinted that this feature eventually could lead to the live migration of VMs between hypervisors.

Networking enhancements include Link Aggregation Control Protocol (LACP) bonding of as many as four NICs, up from two in an active-active or active-passive configuration. This will allow for wider, automatically load-balanced pipes between VMs and stacked Ethernet switches, but it will not increase storage I/O because LACP doesn't offer the ability to reorder packets to communicate correctly with storage systems, official said.

New integration with CloudStack is also planned, including support for provisioning as many as 800 virtual LANs (VLAN) in 10 seconds. Previously the product supported 80 to 100 VLANs. XenServer's WLB can also now send CloudStack recommendations about where to place workloads within the infrastructure.

Finally, Tampa will support EMC Corp.'s VNX array through StorageLink; SAP on Linux running on XenServer; Windows VM paravirtualization drivers, which are based on Microsoft Installer, designed to eventually allow Windows Live Update to upgrade Windows VMs; and new guest operating systems including CentOS, Red Hat Enterprise Linux 6.1 and 6.2, Ubuntu 12.04, and possibly Windows 8.

Beth Pariseau is a senior news writer for and Write to her at or follow @PariseauTT on Twitter.

Dig Deeper on Citrix XenServer

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.