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and troubleshooting. You can use one tool to analyze resource consumption of all
processes running on the system, even though many are in different VEs. After
the problem is understood, you can use the same centralized environment to con-
trol the VEs and their processes.
This global control and observability is nothing new for consolidated systems,
but it provides a distinct advantage over other virtualization models that lack a
centralized environment that can inspect the internals of its guests. Analyzing an
OSV system is not any more complicated than analyzing a consolidated one.
After the resource usage characteristics of a particular workload are known, re-
source management tools should be used to ensure that each VE has sufficient ac-
cess to the resources it needs. Centralized control offers the potential for centrally
managed, fine-grained, dynamic resource management. Most operating systems
already have sophisticated tools to control the consumption of resources in one or
more of these ways:
Assigning CPU time, which is performed by a software scheduler. This con-
trol can be achieved through process prioritization or capping the amount of
CPU time that a process uses during an interval of real time.
Providing exclusive assignment of a group of processes to a group of
processors.
Dedicating a portion of RAM to a group of processes, capping the amount of
RAM that a group of processes can use, or guaranteeing that a VE will be
able to use at least a specific amount of RAM.
Dedicating a portion of the network bandwidth of a network port to an IP ad-
dress or a group of processes, or capping the amount of network bandwidth
used during an interval of time.
Because most operating systems already have the ability to control these resources
with fine granularity, if these controls are extended to the VEs, their resource
consumption can be managed with the same granularity.
Some operating systems include automated features that detect conditions and
take actions. For example, system software might detect that a network service
such as sshd has failed and attempt to restart that service. In the context of re-
source management, dynamic resource controls can be used to react to changing
processing needs of different workloads by changing resource control values on
the fly.
The basic model of OSV assumes that the VEs provide the same operating sys-
tem interfaces to applications as a non-virtualized environment provided by the
host operating system (e.g., system calls). If this similarity can be achieved, ap-
plications need not be modified to run correctly.
 
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