[Wrf-users] Hardware question

[Jan Ploski]

wrf-users-bounces at ucar.edu schrieb am 10/27/2008 07:04:20 PM:

> Good afternoon,
> 
> I am currently in the process of getting hardware quotes for a WRF 
> server but have a question to ask you all.  How hard drive intensive is 
> WRF? Should I be looking at 15K RPM drives, or will 10K or even 7.2K 
> drives work well?

Hello,

I guess it somewhat depends on how many instances you run simultaneously 
(all writing to the same set of disks) and how much data each instance 
produces. The latter in turn depends on the size of your domains and the 
history interval between snapshots. Generally, WRF is CPU rather than IO 
bound.

Maybe this example will help you: one output time slot of a 5km grid over 
Germany with all WRF 2.2 variables included takes ~50 MB of disk space. A 
144h run takes 2.75 hours on 8 Opteron processors. During this run, in 
regular time intervals, 25 slots of 50 MB each are written to disk 
(assuming a 6 hour history interval). So a rather low average data 
throughput is needed (< 1MB/s). It remains far below the disk bandwidth 
even if you reduce the history interval to as low as 0.5h. That said, with 
more output the relative delay caused by disk IO increases, as it does 
when you use more processors per run. I imagine you could also get 
contention if you have multiple runs trying to write to the same disk at 
the same time.

For a more detailed discussion see 
http://www.wrf-model.org/PRESENTATIONS/IO/WRF_IO_test.htm

Regards,
Jan Ploski

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