have more RAM means that the model takes less time wrfems is so run?

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apextreme
Posts: 30
Joined: Mon Apr 05, 2010 7:29 pm

have more RAM means that the model takes less time wrfems is so run?

Post by apextreme » Wed Aug 01, 2012 6:45 pm

Goog morning.
have more RAM means that the model takes less time wrfems is so run?
My computer is:

Ubuntu 12.04 64 bits
Intel® Xeon(R) CPU W3670 @ 3.20GHz × 6 (cores)
6 GB of Memory Ram

I have the option to put 22 GB of RAM, this will make the model run is faster?.
The difference is large or small?
Is it worth spending money to buy more RAM?
Thank you very much!

meteoadriatic
Posts: 1603
Joined: Wed Aug 19, 2009 10:05 am

Re: have more RAM means that the model takes less time wrfems is so run?

Post by meteoadriatic » Wed Aug 01, 2012 8:54 pm

Short answer: it depends.

Longer explanation:

If your current RAM usage during model run is well below total RAM amount, in other words if there is no swapping taking place, then adding more memory won't help improving your run times.

But, there is something more here... if you currently have 1-channel memory configuration and then add new ram modules and convert to 2, 3 or 4-channel memory configuration, then you will get much better memory bandwidth and consenquently you will likely improve model running times significantly. Without knowing your hardware configuration I can't tell if that is the case or not.

Also, if your current domain sizes do not cause memory swapping, but future application could (for example if you create bigger domains, improve resolution, add more nests, or do whatever to cause more RAM usage), then adding RAM could support larger memory needs in future.

pattim
Posts: 199
Joined: Sun Jun 24, 2012 8:42 pm
Location: Los Angeles, CA, USA

Re: have more RAM means that the model takes less time wrfems is so run?

Post by pattim » Fri Aug 03, 2012 4:07 pm

Also, if you have an option for DDR2 vs DDR3 memory, or 1333MHz vs 1600MHz DDR3 memory, the faster the memory the faster your simulations will be. The memory you can use depends (mostly) on your motherboard.

I had 4-channel memory DDR3 1600MHz, but one stick was slightly defective so my BIOS downclocked it to 1333MHz and it worked fine, just slower. Memory speed has become the biggest issue for grid solvers like WRF, GISS ModelE, CESM...

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