[Wrf-users] Wrf-users Digest, Vol 76, Issue 6

[Jonas Kaufmann]

Hello Hein and wrf-help,

thank you for your comments, much appreciated. At the moment I am not
sure whether to spend the extra money on SSD drives or invest in
better / faster processors. If I choose to get SSD drives, I will
report back with some test results.

Best regards,
Jonas Kaufmann

On Wed, Dec 8, 2010 at 10:27, Hein Zelle <hein.zelle at bmtargoss.com> wrote:
> Dear WRF Help,
>
> thanks for the additional comments, good points.
>
>> Just a comment on Hein's comment: there may be another reason he
>> sees the > bottleneck at 64+ CPUs. For a given domain size, the
>> performance will eventually flat out simply because there isn't
>> enough computations to scale up.  There is a balance between
>> computation and communication (via halos for decomposed domains). If
>> one uses nests, then the performance might be limited by the
>> smallest domain.
>
> We verified that on the older xeons it was absolutely memory-bandwidth
> related (big scaling problems already going from 8 to 16 to 32 cores,
> and they disappear with newer nehalems).  However, we have also seen
> the "smallest domain" limitation.  If your smallest domain can't be
> divided up efficiently over the cpu's, you don't gain anything.
>
> This is why we often optimize historical simulations differently:
> - use a relatively small inner domain (e.g. 60x60 grid points)
> - use a maximum of 8 or 16 cores per simulation
> - run multiple simulations in parallel, each doing a historical year.
>
> That's why we often have several parallel simulations at one time.
> This will actually cause bottlenecks on the storage server.  We
> haven't run into network problems (YET!) since we switched to
> infiniband.
>
> Jonas, can you report back if you find out about the SSD performance?
>
> Kind regards,
>        Hein Zelle
>
>
> --
>
> Dr. Hein Zelle
> Advisor Meteorology & Oceanography
>
> Tel:    +31 (0)527-242299
> Fax:    +31 (0)527-242016
> Email:  hein.zelle at bmtargoss.com
> Web:    www.bmtargoss.com
>
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