Wednesday, January 7, 2009

Hypervisor Architecture

Hypervisor Architecture :Hypervisor architecture removes the requirement for a "host" system.
With a hypervisor, virtual machines run on a thin layer of hardware abstraction software.
That software layer, the hypervisor, addresses hardware communications for all
the virtual systems on that machine.
Example : hp VSE
Virtualization does have its dangers, as it incurs greater stress on physical resources.
While under utilization of CPU may be a driving factor to virtualize servers, other
hardware resources may become overtaxed. Given that a host system has limited ability
(depends on application) to page memory used by the guest systems, the most
recognized bottleneck to address is physical memory (RAM). Options to
programmatically alleviate memory bottlenecks incur performance issues when the disk
is re-introduced. Another major component and perhaps less acknowledged is the disk
subsystem. In many cases, depending the purpose and application of the guest/virtual
systems, the disk bottleneck will be the most significant barrier to performance.
Virtual machines are emulating hardware and may not emulate the exact
specifications.
For example, a high end video card may not be emulated in a host system with all the advanced
capabilities.
Disk I/O’s generated from virtual systems (Hosted
Architecture) can suffer from increased software stack processing
Server virtualization establishes a symbiotic relationship, so it is important
to remember that generating disk I/O in one virtual machine slows I/O to the disk from
other virtual systems, no matter the architecture. Fragmentation is both increasingly
substantial in virtual machines environments (hierarchical in Hosted Architecture) and
compounds the disk bottleneck more so than on conventional systems (shared
resource).

Reference: http://files.diskeeper.com/pdf/Virtualization_Performance.pdf

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