Large Hyper-V clusters. Windows Server 8 leaps into VMware territory and beyond with support for as many as 63 hosts and 4,000 VMs per cluster. Backing up the raw numbers are a slew of features that improve performance, manageability, availability, and security in large environments: cluster-aware patching, storage resource pools, thin provisioning, storage offload for data transfers, BitLocker encryption for cluster volumes, data deduplication, and live storage migration.
For the first time, you can team NICs from different vendors, with or without LACP support on your upstream switch. Windows Server 8 also brings Fibre Channel support to Hyper-V guests. You can configure multipath I/O or cluster guests with Fibre Channel for high availability, yet still make use of live migration.
Flexible live migration. Windows Server 8 introduces live storage migration, the ability to migrate virtual hard disks or configuration files for a running VM without interruption. And it removes shared storage as a requirement for migrations. You can now migrate VMs using nothing more than an Ethernet cable; first, the virtual disk is moved, then the running VM. The only requirement is that the hosts belong to the same domain.
There's no longer a cap on the number of migrations you can perform simultaneously, apart from the limitations of your hardware. Windows Server 8 also lets you queue migrations in a single operation that moves VMs one at a time. And you can specify priority VMs to avoid failures when a cluster becomes oversubscribed. If a cluster is loaded with more VMs than it can handle in a failover scenario, Windows Server 8 will shut down low-priority VMs to allow high-priority VMs to run.
Advanced virtual networking. If you've chafed against the lack of promiscuous mode in the Hyper-V virtual switch or pined for the virtual networking capabilities in VMware, you'll be happy to know that Microsoft has dived in with both feet in Windows Server 8. Microsoft seems to have matched the VMware vSwitch feature for feature -- port ACLs, private VLANs, per-vNIC bandwidth reservations, QoS, metering, OpenFlow support, VN-Tag support, network introspection -- all without requiring expensive network devices. The switch will support third-party extensions for inspecting, filtering, modifying, sampling, and inserting packets, with management of the extensions integrated into Hyper-V.