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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: [OT] Allocated memory and VMWare
Date Fri, 15 Jan 2010 14:40:46 GMT
> From: André Warnier [mailto:aw@ice-sa.com]
> Subject: Re: Allocated memory and VMWare
> 
> I may be mistaken, but I do not know of any OS which is capable to run
> with a variable (dynamic) amount of memory.  The amount available is
> usually set when the OS boots, and does not change after that.

In the UNIX/Linux/Windows world, you're correct, but a mature OS is quite capable of dynamically
resizing and moving real memory on the fly.  Our proprietary OS (which does have a JVM) has
been doing it for over 35 years.  Our customers depend on the capability in order to run for
years between reboots.

> I am not the ultimate VMWare expert (yet) (and this is not the right
> forum for that either), but personally I would never configure a VMWare
> server in such a way that the total RAM of the virtual machines really
> running inside it, exceeds the real RAM available on the physical
> machine (minus what the underlying OS and VMWare themselves need).

Unfortunately, that's how all the cloud and other virtualized environments work - there is
massive oversubscription of both memory and CPU, resulting in some "interesting" performance
analysis.

> RAM is cheap.

But virtual RAM is expensive - check out some of the ridiculous cloud pricing options currently
available.

 - Chuck


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