5.1 What Is openMosix?
Basically, the
openMosix software includes both a set
of kernel patches and support tools. The patches extend the kernel to
provide support for moving processes among machines in the cluster.
Typically, process migration is totally transparent to the user.
However, by using the tools provided with openMosix, as well as
third-party tools, you can control the migration of processes among
machines.Let's look at how openMosix might be used to speed
up a set of computationally expensive tasks. Suppose, for example,
you have a dozen files to compress using a CPU-intensive program on a
machine that isn't part of an openMosix cluster. You
could compress each file one at a time, waiting for one to finish
before starting the next. Or you could run all the compressions
simultaneously by starting each compression in a separate window or
by running each compression in the background (ending each command
line with an &). Of course, either way will
take about the same amount of time and will load down your computer
while the programs are running.However, if your computer is part of an openMosix cluster,
here's what will happen: First, you will start all
of the processes running on your computer. With an openMosix cluster,
after a few seconds, processes will start to migrate from your
heavily loaded computer to other idle or less loaded computers in the
clusters. (As explained later, because some jobs may finish quickly,
it can be counterproductive to migrate too quickly.) If you have a
dozen idle machines in the cluster, each compression should run on a
different machine. Your machine will have only one compression
running on it (along with a little added overhead) so you still may
be able to use it. And the dozen compressions will take only a little
longer than it would normally take to do a single compression.If you don't have a dozen computers, or some of your
computers are slower than others, or some are otherwise loaded,
openMosix will move the jobs around as best it can to balance the
load. Once the cluster is set up, this is all done transparently by
the system. Normally, you just start your jobs. openMosix does the
rest. On the other hand, if you want to control the migration of jobs
from one computer to the next, openMosix
supplies you with the tools to do just that.(Currently,
openMosix
also includes a distributed filesystem. However, this is slated for
removal in future releases. The new goal is to integrate support for
a clustering filesystem such as Intermezzo.) |
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