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Re: [K12OSN] Re: [Ltsp-discuss] New LTSP + openMosix How-To

On Wed, Nov 27, 2002 at 07:02:44PM -0800, James Jensen wrote:
> > > >  If a machine is runnning a
> > > > process, for another,
> > > > will that process be nullified if that machine is shutdown?
> > > 
> > > Yes & no, I've done some limited testing, forcing processes to run on
> > > specific nodes (LTSP clients) and then just dropping that node by
> > powering
> > > it off.  In most instances, since the process has vanished with the
> > node
> > > you will see it hang on the system the lost node was running it for. 
> > > Strangely, at other times it keeps right on going.
> > 
> > Have you asked on the mosix lists how that can even happen?
> No, not yet anyway.  In reality it can't happen.  

So we can conclude that it did not happen? :-)

> > > > Basically my question is --> Is is a good idea to use openmosix in
> > > > diskless environment.  If not,
> > > > what is it meant for?
> > > 
> > > That depends on what you are trying to do.
> > > 
> > > 1. Cluster everything (server & clients) in a user production
> > environment? 
> > > I would say no (as much as that pains me to say).  Not unless you're
> > > positive regarding the impact of client nodes dropping out of the
> > cluster
> > > on the rest of your clients...
> > 
> > If you have really fast clients, consider using local apps (not local
> > drives!) instead.
> Why?  Because OpnOff and/or Mozilla don't migrate (or migrate well)?  Moshe
> addressed this a few weeks back.  Forget the magic of migration for
> migrations sake.  It's the *overall* load balance of the cluster that is
> the important factor.  And, this is something that can be measured and
> quatified--for instance, if you are using openMosixview (cluster
> monitoring).

If 95% of the load (CPU and RAM wise) goes to OpenOffice and Mozilla,
then migrating the remaining processes will not help.

Suppose the OO and Mozilla are the to most important applications, the
applications that all users will run most of the time. If the load of
those two application is to be spread, you must do it with other
means. See also my comment on speed below.

> > > 2. Balance the load on the backend, the LTSP server in a user
> > production
> > > environment?  My answer is yes!  This can be achieved quite easily. 
> > And,
> > > since no one had better be turning off your servers you won't lose
> > migrated
> > > processes.
> > 
> > Note that most applications in the "desktop-productivity" class (OO,
> > Mozilla comes to mind) will tend to not migrate. Actually I THINK OO
> > and Mozilla CANNOT migrate because of issues with shared memory. In
> > any case should programs that use much user "realtime" I/O (screen
> > refreshs, sound etc) be *slower* if they do migrate. (Please correct
> > me if I am wrong here James).
> I am happy to report that upon inquiring on openMosix network overhead (a
> question that visits us frequently on this list) the response is a positive
> one:
> Moshe Bar wrote, "...special care was put into making sure that overhead,
> network or otherwise, does not increase as you add nodes. In other words,
> you have the same overhead with 2 nodes or 2000 nodes. Network traffic is
> in all cases, ie worst case, limited to no more then 2% of bandwidth.
> Independent tests and benchmarks by research institutions confirm this."

Sorry but that does not address the problem I was describing. I
thought of a openMosix cluster on a separate subnet, and network
traffic is not the point, but LATENCY is. If the server is not running
the process that a user communicates with, then there will be a delay
before the user gets a response. (It definitely make sense that all
applications reported to "work smoothly" on
http://howto.ipng.be/openMosixWiki/index.php/work%20smoothly are very
computationally intensive).

So I think that many of the applications in the "desktop-productivity"
class will, even if they can migrate, be candidates for "ineffective
migration", or at least that migration will have cost on the user
interation speed.

James, you have a working openmosix cluster, how does say webbrowsers,
word-processing programs and email clients work when they migrate? Do
the feel as fast as if they where running on the server? (Or do they
actually tend to not migrate at all?)


Hans Ekbrand

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