[Go-essp-tech] NetCDF4 compression. write efficiency and CMIP5 policy

[Charles سمير Doutriaux]

Yes I did some testing on the speed and it was much faster to write  
compressed, which did make sense to me since there was so much less  
data to write, and cpu time nothing next to i/o time.

I'll rerun the test again today.

C

On Nov 10, 2009, at 4:50 AM, Dean N. Williams wrote:

> This is not what we experienced. In fact, I recall just the  
> opposite. Charles Doutriaux did the work, so I'll let him respond  
> directly. Also it would be good if Ed Hartnett and Russ Rew respond  
> as well to the slowness that you are seeing. They may be able to  
> help you on this.
>
> Charles, if I recall correctly, were the zlib compressed netCDF  
> files read faster in CDAT?
>
> We are using CMOR2, in which CMOR2 does the DRS, netCDF-4 classic  
> compressed output.
>
> Best regards,
> 	Dean
>
> On Nov 10, 2009, at 4:20 AM, <stephen.pascoe at stfc.ac.uk> wrote:
>
>> Hi Dean
>>
>> In tests we've done at BADC we have experienced 10-20x slowdown in  
>> write speed with NetCDF4 compression.  Is this typical and are  
>> modelling centres aware that they can expect a significant I/O  
>> bottleneck?
>>
>> This makes me think, have we said CMIP5 data *must* be compressed?   
>> Is there a danger we will get a higher volume of data than we  
>> expect because it will be uncompressed to speed up the process at  
>> the modelling centres?  How would we enforce NetCDF compression --  
>> presumably it would be discovered during replication.
>>
>> Cheers,
>> Stephen.
>>
>> ---
>> Stephen Pascoe  +44 (0)1235 445980
>> British Atmospheric Data Centre
>> Rutherford Appleton Laboratory
>>
>>
>> -- 
>> Scanned by iCritical.
>>
>>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/go-essp-tech/attachments/20091110/2cf24565/attachment.html