[Beowulf] single machine with 500 GB of RAM

Andrew Holway andrew.holway at gmail.com
Wed Jan 9 06:28:23 PST 2013

> So if I am using a single socket motherboard, would that not be faster or does
> a single CPU not cope with that amount of memory?

I am not aware of a single socket motherboard that can cope with 500GB
ram. 2 socket motherboards support about 256GB (128GB per processor)
or so at the moment and quad socket boards upto 1TB.

You will need the 2nd CPU in order to address the memory in the 2nd
banks of ram. 3rd CPU for the 3rd banks of ram etc so your extra CPUS
just become memory controllers.

This type of setup generates a lot of cross calls (xcalls). So, when
CPU1, where your application is running, requires something from 2nd
bank of memory it must request it from CPU2. These types of calls can
be quite slow latency but I believe the bandwidth is no so bad.
Therefore, if your memory requests are comparatively quite large you
should be sitting pretty.

I think this is also the same for ScaleMP. If you have many tiny
memory accesses it will suck but it can be quite nice if your memory
objects are large.

You will probably need to spend around 15k GBP whatever you do. Ask
any reputable system builder for a 500GB box and you'll probably get
lots of nice offers for a Supermicro beast. If your system builder is
really nice they might have a system for you to test on.

Greetings from a grey Berlin.


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