[Go-essp-tech] +2Gb CMIP5 files

stephen.pascoe at stfc.ac.uk stephen.pascoe at stfc.ac.uk
Tue May 18 08:34:14 MDT 2010 

I've done some testing of these file limits this afternoon and I don't
think the filesystems will be a problem.

>From Wikipedia it appears the FAT32 file system has a 4Gb limit
(http://en.wikipedia.org/wiki/File_Allocation_Table).  That covers
Windows 95 onwards but my Windows XP box is NTFS and has no problem with
+4Gb files.  Similarly my 32-bit linux laptop (recent ubuntu) can handle
+4Gb files.

Looks like anyone with a reasonably modern system will be able to handle
+4Gb files.  We may have more problems with old NetCDF library versions.

S.

---
Stephen Pascoe  +44 (0)1235 445980
British Atmospheric Data Centre
Rutherford Appleton Laboratory

-----Original Message-----
From: go-essp-tech-bounces at ucar.edu
[mailto:go-essp-tech-bounces at ucar.edu] On Behalf Of
ag.stephens at stfc.ac.uk
Sent: 18 May 2010 09:31
To: taylor13 at llnl.gov; go-essp-tech at ucar.edu
Cc: doutriaux1 at llnl.gov
Subject: Re: [Go-essp-tech] +2Gb CMIP5 files

Dear Karl,

Whether we think it's advisable or not, I'm sure that some of the wider
CMIP5 user community will be looking at the outputs on Windows. I think
it is sensible to set a 2GB file size limit.

Regards,

Ag 

-----Original Message-----
From: go-essp-tech-bounces at ucar.edu
[mailto:go-essp-tech-bounces at ucar.edu] On Behalf Of Karl Taylor
Sent: 17 May 2010 18:45
To: go-essp-tech at ucar.edu
Cc: Doutriaux, Charles
Subject: Re: [Go-essp-tech] +2Gb CMIP5 files

Dear all,

CMOR has code already in place for checking whether a file exceeds 2 GB,
but it is currently turned off (it was turned on for CMIP3).  We thought
it was now unnecessary.  If the feeling is that there will be users
downloading CMIP5 files to windows machines using older operating
systems, I suppose that limiting CMIP5 files to whatever the limit is (2
GB or 4 GB -- does anyone know which it is?) might be wise.

On the other hand, will anyone use a windows machine to look at netCDF
files?  If not, maybe this is a non-issue.

Karl

On 5/16/10 12:08 PM, stephen.pascoe at stfc.ac.uk wrote:
> I think I raised undue alarm here when suggesting we might be dealing
with +2GB files.  Thanks Phil for clarifying that UKMO is still planning
to limit itself to<2GB files.
>
> I am wondering what the policy should be here?  My first thought is
that modeling centres will mainly make the same decision as UKMO since
it is in their interest for their model output to be widely used.
However, enforcement could be difficult.  The logical place to enforce
the limit is in the level 1 QC but CMOR doesn't do this so it will be a
problem for people running datanodes.
>
> I suggest we make a strong recommendation to supply data in<2GB files
and enforce it during level-2 QC before replicating.
>
> S.
>
> -----Original Message-----
> From: go-essp-tech-bounces at ucar.edu on behalf of Michael 
> Lautenschlager
> Sent: Sun 5/16/2010 1:35 PM
> To: V. Balaji
> Cc: go-essp-tech at ucar.edu
> Subject: Re: [Go-essp-tech] +2Gb CMIP5 files
>
> Hello *,
>
> we strongly support Phils decision for data files less than 2 GB. We 
> made decision in Hamburg for the same reasons because we cannot expect

> that all users use 64 Bit systems. Most Windows environments are still

> running with 32 Bits.
>
> Best wishes, Michael
>
> ---------------
> Dr. Michael Lautenschlager
>
> German Climate Computing Centre (DKRZ) World Data Center Climate
> (WDCC)
> ADDRESS: Bundesstrasse 45a, D-20146 Hamburg, Germany
> PHONE:   +4940-460094-118
> E-Mail:  lautenschlager at dkrz.de
>
> URL:    http://*www.*dkrz.de/
>           http://*www.*wdc-climate.de/
>
> V. Balaji schrieb:
>    
>> If I understood correctly the most serious 2Gb problem is with
apache!
>>
>> Bentley, Philip writes:
>>
>>      
>>> Hi Stephen,
>>>
>>> Yes, that's true, we did create a small number of test netCDF files 
>>> in that size range. But this was because the CMOR library we used at

>>> the time didn't include functionality for chunking the output into 
>>> smaller files. Plus we wanted to stress-test our pipeline!
>>>
>>> Two things have happened since then:
>>>
>>> 1. Jamie has been working with Charles at PCMDI to implement and 
>>> test a solution whereby we can limit the size of the output netCDF 
>>> files produced by CMOR.
>>>
>>> 2. We have made the local decision to limit our netCDF file sizes to

>>> 2 GB (or thereabouts) as, logistically, that will cause us less 
>>> headache moving these files around, and it should maximise the 
>>> number of client applications in which the files can be read.
>>>
>>> IIRC, I think Balaji mentioned that the 64-bit offset format was 
>>> required for output from the gridspec toolset. I could be wrong.
>>>
>>> Regards,
>>> Phil
>>>
>>>        
>>>> -----Original Message-----
>>>> From: go-essp-tech-bounces at ucar.edu 
>>>> [mailto:go-essp-tech-bounces at ucar.edu] On Behalf Of 
>>>> stephen.pascoe at stfc.ac.uk
>>>> Sent: 14 May 2010 10:52
>>>> To: go-essp-tech at ucar.edu
>>>> Subject: [Go-essp-tech] +2Gb CMIP5 files
>>>>
>>>> The latest UKMO extraction for CMIP5 has produced some files in the

>>>> 30Gb range.  We had discussed previously the assumption that all 
>>>> files would be<2Gb.  Do we feel it is important to enforce a<2Gb 
>>>> limit or should this just be a recommendation on modelling centres?
>>>>
>>>> To my knowledge there is two issues with +2Gb files:
>>>>
>>>>   1. +2GB NetCDF files will be in 64-bit offset format.
>>>> Therefore NetCDF libraries prior to v3.6 will not be able to read 
>>>> them.
>>>>   2. Older file systems may have a 2Gb file limit. This will mainly

>>>> affect 32-bit systems that are a few years old. FAT32 has a 4Gb 
>>>> limit.
>>>>
>>>> These are end-user issues, is there any reason why the ESG software

>>>> might have problems with files over 2Gb?  If we do want to ensure 
>>>> files are<2Gb do we want to mandate the modelling centres deliver 
>>>> that or will the data centres need to split files?
>>>>
>>>> Stephen.
>>>>
>>>> ---
>>>> Stephen Pascoe  +44 (0)1235 445980
>>>> British Atmospheric Data Centre
>>>> Rutherford Appleton Laboratory
>>>> --
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