Out of Core Memory Mode

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  • Last Post 20 September 2018
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mc4167 posted this 19 September 2018

Hello, 

I wanted to ask a few questions regarding HFSS. Specifically, I wanted to ask for some clarification on what exactly does "out-of-core" mode does, and are there settings regarding "out-of-core" mode that we can access/modify. Currently in HPC options I only see the option to either enable to disable "out-of-core" mode, but no other settings. Additionally, for larger simulations, for example requiring 64 GB of RAM or more, would it also be possible to run these simulations instead with less memory (less than 64 GB) and a large SSD? Specifically, what is the difference/benefit of solving purely on RAM versus using smaller RAM in conjunction with a large SSD?

Thank you.

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SandeepMedikonda posted this 20 September 2018

Moved to the Electromagnetics group and added a few tags so that it might get more attention. 

peteroznewman posted this 20 September 2018

Hello,

I don't use HFSS, but I do understand these issues in the Structural solvers and I think the terminology is the same.

Solving a small model can be done in-core, which means all in RAM.

When the solver can't fit a large model entirely in RAM, it uses an out-of-core method that uses the HDD or SSD storage to hold parts of the solution while it is working.

Obviously a SSD is faster than a HDD, so using a SSD will reduce your wait time. But DRAM is faster than a SSD by at least a factor of 10 or more.

So to minimize solve time, install more RAM rather than using a SSD.  If you have the money, also get a SSD to reduce the time spent booting Windows, loading ANSYS and opening and saving models.

It sounds like the HPC option to disable out-of-core is like a flag I can set for the Structural solver to force it to solve in-core when it would choose out-of-core on its own.  That flag is useful when the model actually does fit in RAM, but the solver makes a conservative estimate on whether it will fit in RAM or not. If you force it to run in-core and it doesn't actually fit, then the solver crashes part way through the solution.

Regards,

Peter

 

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