With WinHEC 2007 around the corner, Microsoft has reset expectations for Windows Server Virtualization, code-name...
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A Viridian beta version will indeed ship with Windows Server "Longhorn" RTM (release-to-manufacturer) in the second half of this year, said Microsoft general manager for virtualization Mike Neil in a blog, but it will be stripped of many important features.
Features Microsoft has removed from the initial Viridian beta include:
- Live migration, functionality akin to VMware's VMotion;
- Hot add of resources such as storage, networking, memory and processor;
- Support for more than 16 logical processors or cores.
Neil cited time and resource constraints, plus pressure to ship, as reasons for Viridian's feature slip. He was noncommittal about a timeframe for release of those features, simply stating that they had been postponed "to a future release of Windows Server virtualization."
At the same time, Neil cited several tantalizing Windows Server virtualization features that may make the technology worth waiting for. Among them: Full support for virtualization-enhanced chips like Intel-VT and AMD-v, a 64-bit hypervisor, up to 32 GB of RAM per virtual machine, native support for Microsoft Cluster Server and Volume Shadow Services (VSS) and integration with System Center Virtual Machine Manager, to name a few.
The loss of live migration
Live migration – the ability to non-disruptively move a running virtual machine between virtualization hosts – is widely regarded as the cornerstone of any sophisticated virtualization platform. Take VMware VMotion, the granddaddy of live migration. In and of itself, VMotion is useful when doing planned maintenance; combined with VMware Distributed Resource Scheduler (DRS) and VMware High Availability, VMotion enables important automated load balancing and high availability capabilities.
"We believe live migration is a critical to building a dynamic data center," said Chris Barclay, director of product management at virtualization platform provider Virtual Iron Software Inc., in Lowell Mass. "It's a significant feature for them to delay."
Virtual Iron supports live migration in its product suite. Similarly, XenSource is in the process of productizing live migration of Windows and unmodified Linux guests for its next XenEnterprise product, expected shortly. The open-source Xen code based has supported "live relocation," in Xen parlance "since we started the company," said Simon Crosby, XenSource CTO.
Without live migration, Crosby said, Microsoft virtualization users will be limited to using virtualization for server consolidation.
Crosby lamented the other cuts to Viridian's feature set, hot-add of system resources and a 16 processor limit.
When it came to the number of cores, Crosby said the key question is: "When Viridian ships, what will the industry standard server have on it?" The limit of 16 logical processors maps to the midrange x86 servers today – four processors and four cores.
Being able to dynamically add virtual CPUs, memory and disk meanwhile, "is very important for a resource assignment and HA perspective," Crosby said. "For server consolidation, you want to do a great job optimizing the utilization of the box – it's actually quite important."
Virtualization and operating system lockstep
Microsoft's decision to drop key Viridian features underscores the difficulty of developing a virtualization platform in tandem with an operating system.
"With all the venture capital dollars sloshing around, there's no lack of capital," said Mike Grandinetti, chief marketing officer at Virtual Iron. But Microsoft's inability to ship these features on time demonstrates that "the amount of computer scientist capable of solving these problems isn't growing."
No matter how many resources you have, it's a difficult problem to solve, Crosby said – one that Red Hat will struggle with as well as it works to develop the Xen virtualization shipping in Red Hat Enterprise Linux 5. "You have these two trains moving on separate tracks; the challenge is combining them in to one."
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