Server Virtualization Buying Guide -- Hyper-V
VMware might be the dominant force when it comes to server virtualization, but since its release more than three years ago, Microsoft's Hyper-V hypervisor has rapidly developed into a credible, low-cost alternative.
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Microsoft's Hyper-V Server 2008 R2 is a small footprint hypervisor for server virtualization, which you can download free, and which you can run on x64 compatible processors with Intel VT or AMD-V technology enabled. But unlike VMware's free vSphere hypervisor, Microsoft's free hypervisor contains important features, such as Live Migration (equivalent to VMware's vMotion) and dynamic memory (see below.) It is designed as an entry-level server virtualization product for small businesses with half a dozen or so servers, and it currently accounts for about 10 percent of all Hyper-V implementations, according to the company. There are some limitations though: In particular, the hypervisor lacks a local graphical user interface, and it must be managed from the command line.
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Microsoft's Hyper-V virtualization platform is "an integral part of Windows Server 2008 R2," as Microsoft puts it, so the way to "buy" Hyper-V is to license and install a copy of the server product and then install the Hyper-V role. This effectively installs the Hyper-V hypervisor on to your server bare metal, with Windows Server running on top of it in a privileged parent partition. You can then install guest operating systems into child partitions.
In its latest version, available in Windows Server 2008 R2 SP1, the hypervisor offers many features, including:
- Live Migration -- When Microsoft first released Hyper-V, this feature was known as Quick Migration because VMs had to be stopped, albeit briefly, as they were moved from one host to another. With Live Migration you can move VMs between hosts without any interruption, providing a similar capability to VMware's vMotion. (Hyper-V is still not able to offer an equivalent feature to VMware's Storage vMotion, which enables you to move a VM file from one storage device to another while the VM is running -- although this is slated to be included in Hyper-V 3 in Windows Server 8, expected to be released in 2012.)
- Dynamic memory -- This lets you change the RAM allocated to individual VMs on a Hyper-V host while they are running, in response to changing workloads on these VMs.
- Dynamic VM storage Hyper-V -- This supports hot plug-in and hot removal of Virtual Hard Drive (VHD) files and pass-through disks while a VM is running.
- Network Load Balancing -- Hyper-V has virtual switch capabilities, and you can configure virtual machines to run with Windows Network Load Balancing (NLB) Service to balance loads across all your virtual machines on different servers.
- Virtual machine snapshotting -- Snapshotting captures the entire state of a running VM, making it possible to revert a machine quickly back to an earlier state.
- Disaster recovery -- This is provided using the clustering features in Windows Server, across the data center, and, in theory, between data centers.
- Linux guest support -- Hyper-V supports SUSE Linux Enterprise Server 10 with SP4 or version 11 with SP1, and Red Hat Enterprise Linux versions 5.2-6.1, CentOS 5.2-6.0
- Management options include WMI, the standard Microsoft Management Framework, and Microsoft System Center Virtual Machine Manager.
Windows Server 2008 R2 comes in three different editions: Standard, Enterprise and Datacenter. The Standard and Enterprise editions are licensed on a per-server basis, while Datacenter is licensed on a per-processor basis.
This obviously has important implications when it comes to licensing costs, but there is another important difference that can affect costs: the guest virtualization rights included in the host server license. You can use a Standard edition license to run either Windows Server without virtualization, or, if the Hyper-V role is installed, the Hyper-V host plus a single virtual instance of Windows Server. With the Enterprise edition you are licensed to run the host plus four virtual instances of Windows Server, while the Datacenter edition allows you to run unlimited instances of Windows Server running on the host. Therefore, a physical machine hosting eight Windows Server guests would require you to buy two Enterprise licenses or a single Datacenter license. (All licenses allow Hyper-V to host an unlimited number of non-Windows VMs, up to the technical limits.)
Due to differences in the features included in the editions of Windows Server, the Standard edition has slightly fewer virtualization capabilities. In particular, you can't use the Standard edition in high availability configurations (in other words, there's no host clustering, application failover or Live Migration), and you can't have more than 32GB memory or more than four physical processors on the host.
Hyper-V Feature Comparisons
|Logical Processors (cores or hyperthreads)||64 LP||64 LP||64 LP|
|Physical Memory Support||Up to 32 GB||Up to 1 TB||Up to 1 TB|
|Max No. of VMs||8 V-Procs per LPor 384 VMs, whichever is lower (all editions)|
|VM Licensing||1 Per License||4 Per License||Unlimited|
VMware vs. Microsoft virtualization platforms compared:
|Hypervisor Management||vCenter||various, including System Center Virtual Machine Manager|
|High Availability/Failover||vCenter||Windows Server clustering|
|VM Migration||vMotion||Live Migration|
|VM Storage Migration||Storage vMotion||Not available until Hyper-V 3.0, due 2012|
|Licensing||per processor plus vRAM||per server or per proc (Enterprise edition)|
Private clouds using Hyper-V
Where VMware offers a dedicated software stack for building private and hybrid clouds, Microsoft uses existing product families -- especially its System Center management suite -- to manage physical and virtual machines and enable Hyper-V be used as the hypervisor at the center of a cloud infrastructure.
Microsoft's private cloud solution is licensed through the Enrolment for Core Infrastructure (ECI) Datacenter licensing program. This includes:
- Windows Server Datacenter, which supports unlimited Windows Server virtualization rights.
- System Center Server Management Suite Datacenter (SMSD), which includes rights to manage an unlimited number of physical or VMs. SMSD features Configuration Manager, Operations Manager, Data Protection Manager, System Center Orchestrator, and, crucially, Virtual Machine Manager (VMM), including VMM Self-Service Portal. You can use Virtual Machine Manager to manage Hyper-V environments and virtual machines running on VMware's ESX/ESXi and Citrix's XenServer hypervisors.
- Forefront Endpoint Protection for an unlimited number of virtual machines.
You can use this cloud stack to create the usual notion of a private cloud that includes pooled resources and provisioning of services through a self-service portal. Features like chargeback or "showback" are available through third-party extensions to System Center, such as VKernel's vOPS Reporting and Chargeback. Eventually, it will be possible to migrate some or all of an application service from a private cloud to Microsoft's Windows Azure public cloud platform.
Because ECI Datacenter is licensed on a per-processor basis and allows for an unlimited number of VMs in a cloud environment, it carries a substantially lower cost than a system of the same scale built using VMware's cloud stack, which includes per-VM charges for vCloud, vCenter and vShield as well as, indirectly, for vSphere. Figures put together by Microsoft show that on a cluster of 42 physical hosts with 84 sockets supporting 504 VMs (six VMs per processor), the Datacenter ECI license would cost you $388,000, compared to $1.87 million for the VMware solution. If the consolidation ratio on each physical processor is increased to 15:1, then while Microsoft's cloud solution cost is unchanged, the cost of the VMware solution would rise to $3.3 million.
There's no doubt that Hyper-V is not -- yet -- as mature or feature-rich as VMware's virtualization platform, but it is catching up fast. Its lower costs mean that for Windows shops it is increasingly becoming a viable alternative to the market leader.
Paul Rubens is a journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.
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