Type 1 and Type 2 Client Hypervisors
This post is based on insight gained from two of Brian Madden’s posts: A deeper look at VMware’s upcoming bare-metal client hypervisor and Bare-metal client hypervisors are coming — for real this time
Type 1 Hypervisor
Type 1 (or native, bare-metal) hypervisors are software systems that run directly on the host’s hardware to control the hardware and to monitor guest operating-systems. A guest operating system thus runs on another level above the hypervisor. Some examples are VMware ESX, Xen, Microsoft Hyper-V, etc.
Type 1 hypervisors are appropriate when you want to provide the only OS that is used on a client. When a user turns a machine on, he only sees a single OS that looks and feels local.
Type 2 Hypervisor
Type 2 (or hosted) hypervisors are software applications running within a conventional operating-system environment. Considering the hypervisor layer as a distinct software layer, guest operating systems thus run at the third level above the hardware. Some examples are VMware Workstation, VMware Fusion, MED-V, Windows Virtual PC, VirtualBox, Parallels, MokaFive, etc.
Type 2 hypervisors are appropriate when you want a user to have access to their own local desktop OS in addition to the centrally-managed corporate VDI OS. This could be for an employee-owned PCscenario, or it could be a situation where you have contractors, etc., who need access to their personal apps and data in addition to the company’s apps and data.
Over the past 5 years, Type 1 hypervisors are dominantly used in the server market, whereas, Type 2 hypervisors are being used on clients, i.e., desktops and laptops. Recently, the need for a Type 1 hypervisor that runs locally on a client device, called the client hypervisor, has emerged for supporting the Virtual Desktop Infrastructure VDI).
VDI’s promise lies in realizing a significant cost reduction for managing desktops. A client hypervisor is useful because it combines the centralized management of VDI with the performance and flexibility of local computing. It offers several advantages:
- It provides a Hardware Abstraction Layer so that the same virtual disk image can be used on a variety of different devices.
- The devices do not need a “base OS” when the client hypervisor is present. The maintenance overhead of patching a “base OS” frequently on each of the devices is greatly reduced.
- Once a virtual disk image has been provisioned, it runs and the display is driven locally. This frees up the client from the need to support remote display protocols.
- It decouples the management of the device from the management of Windows and the user; administrators can spend their time focusing on user needs instead of device maintenance.
Type 1 Server and Client Hypervisors
Server hypervisors are designed to make VMs portable and increasing the utilization of physical hardware. Client hypervisors are intended to increase the manageability of the client device and improve security by separating work and personal VMs.
The bottom line is that even though they’re both called “Type 1” or “bare-metal hypervisors,” there are some philosophical differences in how each came to be. (This could help explain why it has taken over five years to extend the Type 1 hypervisor concept from the server to the desktop.)
|Dimension||Type 1 Server Hypervisor||Type 1 Client Hypervisor|
|Design Goal||Host multiple VMs and make each VM seem like a “real” server on the network.||The user shouldn’t even know that there is a hypervisor or they are using a VM.|
|Virtualization Goal||I/O: Disk and Networking||Native device support that affects user experience, e.g.,
a) GPU and graphics capabilities
b) USB ports and devices
c) Laptop battery and power state
d) Suspend/Hibernate states
|Tuning||Maximum simultaneous network, processor and disk I/O utilization||Graphics, multimedia and wireless connectivity|
|Hardware Support||Narrow set of different preapproved hardware models||Should (ideally) run on just about anything|
|Intrusiveness||Controls most if not all of the hardware platform and devices and provide a near complete emulated and/or para-virtualized device model to the virtual machines running on top||a) Should support full device pass-through to a guest VM.
b) Should also support dynamic assignment and “switching” of devices between different guests
Type 1 Client Hypervisor Vendors
In the Type 1 client hypervisor space, there are Neocleus NeoSphere and Virtual Computer NXTop. There are product announcements from both VMware and Citrix, however, there is no shipping product to date. There is also the Xen Client Initiative – an effort to port the open source Xen hypervisor to the client.
Today, hypervisors are a commodity. While they are indeed foundational technology, they are “out of sight is out of mind”, i.e., most users do not perceive their presence and hence ascribe no/low value for this technology. Hypervisor developers will be hard pressed to build a lasting public company solely based on selling hypervisors.