High availability and VM clustering in Hyper-V worked well in the lab, but Hyper-V lacks a few fundamental features compared with ESX and the VirtualCenter/ VirtualInfrastructure suite. First, in order to cluster VMs with Microsoft Cluster Service, VMs must live on different logical unit numbers (LUNs) because it's not possible for two separate Hyper-V virtual machines to have read/write access to a file system at the same time. With VMware's VMFS, middleware exists between a VMware VM and the back-end LUN. As a result, the shim abstracts the back-end storage and allows multiple VMs and ESX servers to share a single LUN. This isn't a huge deal for small shops, but the need to provision separate LUNs for each virtual machine will be an administrative nightmare, especially for IT shops that routinely build and destroy VMs for testing, development, and quality assurance.
Microsoft told us that shared storage support for multiple VMs exists now through a third-party offering, Kayo FS from Sanbolic. Kayo FS is priced at $299 per host server and is sold in bundles of five licenses. Conversely, VMFS comes free with ESX Server, and it's included with all VMware Infrastructure versions.
Disaster recovery is the other big deal for enterprises virtualizing in production. Hyper-V does it well, but not quite as quite as well as VMware's VMotion. In Hyper-V, when a VM must be relocated to separate physical hardware, the VM state and storage must be saved and relocated, and there's downtime associated with that process. With VMotion, state and storage are migrated in the background, and the cutover is almost instantaneous. Pricier versions of Citrix XenServer offer similar Live Migration capabilities. In the labs, we've seen VMotion cutovers happen in less than one second. With Hyper-V, the time it takes to cut over a virtual machine to new server hardware depends on the amount of memory allocated to the VM, along with the amount of storage that must be copied.
On the flip side, VMotion is only available with VMware Infrastructure Enterprise, the most expensive edition. Similarly, you'll need to buy Citrix XenServer Enterprise or Platinum edition in order to get Live Migration.
For now, Hyper-V's strengths are confined to server consolidation and basic enterprise management. But enterprise IT needs more than just a hypervisor, and VMware/ Citrix have the edge in load balancing, disaster recovery, high availability, rapid provisioning, and guest OS support.
But you can bet the VMware and Citrix advantage will be short-lived. Service Center Virtual Machine Manager 2008 promises new features like support for VMware's Virtual Machine file format through an integration with VirtualCenter. A ton of resources are being pumped into Hyper-V development, and that usually spells trouble for Microsoft's competitors.