Re: What's the difference between openmosix and PBS system?

On 09:27 Wed 19 Jul     , ???? wrote:
>     Openmosix makes a cluster into a logical SMP machine so that
>     users can submit job easily and the job control, resource
>     scheduling will be handled by openmosix but, this is exactly the
>     same thing PBS system covers. I mean, if I install an openpbs on
>     my cluster, I can also submit my serial/parallel job
>     smoothly. So why should I use openmosix? 

While having similar aims, the way batch systems like the grid engine
achieve them is quite different from the openMosix approach. Roughly
speaking, batch systems start jobs on free nodes by "ssh-ing" to the
given node (or do something a bit more clever but still somehow
equivalent). This is also the reason why they have bring their own job
management tools (e.g. qstat, qsub etc.) -- jobs just have to be
processes on your local node. This does also limit the kind of jobs
you can use with batch systems, as they're usually unable to execute
interactive or X applications.

Contrary to that, openMosix engages in a much lower level. It is a
kernel patch that allows processes running locally on a node to be
transmitted to another node transparently during runtime. The last
part is quite important, as it has some interesting consequences:

 * If there is a load inequality among the cluster nodes, it can be
   equalized much smoother by simply migrating some jobs to the idling
   machines within seconds. Batch systems can only equalize load by
   starting new jobs which isn't as elegant and, more important, will
   fail if the queue is empty.

 * You don't have to use special job management tools, as openMosix
   can migrated nearly every process on your node (ok, there are some
   limitations: no multithreading, no shared memory, but for oM's use
   case this is a weak limitation).

 * oM does also work with interactive and X applications. For instance
   if you have a graphical fractal generator which is creating high
   load on your login machine, oM could easily migrate it to an idling
   machine without you noticing it.

So, oM is, despite some limitations, way more elegant. Give it a try.

Cheers!
-Andreas

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