Storage vendors keen to integrate with XenServer

Years after implementing its first storage integration with Symantec, Citrix Systems is making integration and automation with data storage products a major priority for its XenServer 5.5 server virtualisation software due to ship next month.

Citrix Systems said this week that more than 20 storage partners are in its Citrix Ready Open Storage Program. The program's purpose is to verify that data storage products work with XenServer through its StorageLink technology. StorageLink consists of components that tie storage resources to virtual servers.

Dell Inc./EqualLogic, Hewlett-Packard (HP) Co. and NetApp have completed work writing code to integrate disk arrays with the StorageLink API for XenServer. New partners working to integrate with StorageLink for XenServer 5.5 include Acronis Inc., Brocade, CA, CommVault, Compellent, DataCore Software Corp., Emulex Corp., FalconStor Software Inc., Hitachi Data Systems, InMage Systems Inc., LSI Corp., Microsoft Corp., PHD Virtual Technologies, Pillar Data Systems, QLogic Corp., Reldata Inc., Vizioncore Inc. and Xiotech Corp.

XenServer 5.5 will also add a new API for backup software vendors, with the goal of creating consolidated backup via server images loaded onto a proxy server similar to VMware Inc.'s VMware Consolidated Backup (VCB).

An effort to boost XenServer adoption

XenServer already operates according to traditional block-based storage paradigms, assigning one virtual machine to each logical unit number (LUN) on shared storage. Several storage vendors, including DataCore, EqualLogic, NetApp and Symantec have already been certified as generally compatible with XenServer within Citrix.

However, Chris Wolf, senior analyst, data center strategies at Midvale, Utah-based Burton Group, said Citrix Systems has struggled to gain market share against VMware and its proprietary Virtual Machine File System (VMFS) clustered file system in part because it lacked integration with storage arrays that would allow server admins to quickly deploy virtual machines.

"In a VMFS volume, all virtual machines are stored on one big LUN and new virtual machines are just deployed into it. [Without StorageLink] they have to go to the SAN admin and request a new LUN every time they want to deploy a virtual machine," Wolf said, who is also a XenServer 5.5 beta tester.

This can drive up the total cost of ownership (TCO) in management time or overprovisioned storage space.

"StorageLink helps with the TCO story," Wolf said.

Data storage vendors have complained in the past that VMFS steps on their product-differentiation toes, and "it's true VMFS does strip out some intelligence features in the array," Wolf said. VMware users looking ahead to VMware's vSphere 4 release said storage remains a top challenge in virtual server environments.

But the market share picture still indicates that this hasn't been a deal-breaker for users. In the meantime, VMware has beefed up feature parity in its Raw Device Mapping (RDM) and opened new storage APIs to array partners.

"Storage is the hardest part of VMware [deployments], and Citrix may have theoretical arguments about why they can do it better," said Andrew Reichman, a senior analyst at Cambridge, Mass.-based Forrester Research Inc. "But there are a lot of politics, and storage is complicated to get right no matter what you do."

Coopetition with EMC?

The Citrix Essentials management console supports XenServer and Microsoft's Hyper-V hypervisor. A version of Citrix Essentials for Hyper-V incorporating StorageLink "adapters" for some vendors' arrays has been shipping since April 7.

There are mixed signals when it comes to the participation of rival VMware's parent company EMC Corp. in the StorageLink program. A Citrix spokesperson said EMC's Clariion CX3 and CX4 storage systems support Essentials for Hyper-V, as do HP's StorageWorks MSA 2000 and EVA 4400/6000/8000, and NetApp's FAS/S/V Series arrays.

In an email to SearchStorage.com to answer a question about its StorageLink involvement, an EMC spokesperson wrote "we … support Xen from RedHat and Novell. If we see demand for the Citrix derivative, we'll support it in the future."

The Citrix Systems spokesperson countered in an email that "the EMC certification [on Citrix Essentials for Hyper-V] was done by Citrix in the EMC labs in Redmond, [Wash.] per EMC's specifications for product certification. Regardless of whether EMC is going to choose to promote it, this certification benefits our customers and gives them a choice."

"I expect you'll see EMC included in the next wave of [ announcements about StorageLink," Burton Group's Wolf said. "Citrix isn't stupid – they're not necessarily going to go to the VMware parent company before the first release and share all their ideas."