[MITgcm-support] rbcs advice

[Martin Losch]

Hi Jody,
I am not sure if I understand all of the issues, but here’s my 5-cent worth:

- Can you reduce the file size by using single precision input (in data: readBinaryPrec = 32)? This would mean that all of your input files (topgraphy, initial conditions, surface forcing, etc.) need to be converted to single precision, but it would save you 50% of the disk space, if you can live with the loss of precision. For smaller files, there’s always OBCS, but that comes with a different set of issues (as you know).

- I can imagine that reading 6GB chunks from 150-300 GB files can be slow, but that would be my only concern with the single files.

- I haven’t used this feature of RBCS yet, but from looking at the code (rbcs_fields_load.F), it looks to me as if the same counter variables initer0 and initer1 are used for reading the record number from a large file and for generating the name of the individual files:
        IF ( rbcsSingleTimeFiles ) THEN
         IL=ILNBLNK( relaxTFile )
         WRITE(fullName,'(2a,i10.10)') relaxTFile(1:IL),'.',initer0
         CALL READ_REC_XYZ_RS(fullName, rbct0, 1, myIter, myThid)
         WRITE(fullName,'(2a,i10.10)') relaxTFile(1:IL),'.',initer1
         CALL READ_REC_XYZ_RS(fullName, rbct1, 1, myIter, myThid)
        ELSE
         CALL READ_REC_XYZ_RS(relaxTFile,rbct0,intime0,myIter,myThid)
         CALL READ_REC_XYZ_RS(relaxTFile,rbct1,intime1,myIter,myThid)
        ENDIF

So I think that you files names (in your example) should look like this:
Uforce.0000000000
Uforce.0000000001
Uforce.0000000002
…
Uforce.0000000024 (or 48)
totally independent of your time step. It’s just the large file with 24 records in it split into 24 individual files with the record number in the name.

Martin

On Mar 4, 2014, at 1:30 AM, Jody Klymak <jklymak at uvic.ca> wrote:

> 
> Hi all,
> 
> I have been using RBCS package to force a coarse domain with internal waves, and that works very well.  Now I want to nest the larger domain into a small domain.  I'm fine w/ a 1-way nest (I don't expect the small scale will substantially impact the large-scale).  
> 
> My issues are how to deal with rbcs.  Each field in the domain as doubles will be 6 Gb/time step. I'd like to have at least 24 forcings over two tidal cycles (48 would be better), so we are talking about 150-300 Gb files for the relaxTFile etc.  
> 
> Is that OK, or should I be saving the files separately, using rbcsSingleTimeFiles = .TRUE.
> 
> If I do rbcsSingleTimeFiles = .TRUE., then I am unsure how to specify the iteration number.  I found the discussion in the manual vague.  By "iteration" do we mean the iteration number for the saves? Or model iteration number? Or???
> 
> i.e. suppose I have 
> 
> deltaT=12.
> deltaTrbcs=3600.
> 
> and I have snapshots I want to use to force at t=0,3600,7200, etc
> 
> I'd think I need to set 
> 
> rbcsForcingOffset=-1800.
> and the files would be:
> Uforce.0000000000
> Uforce.0000000001
> Uforce.0000000002
> 
> or would they be
> Uforce.0000000000
> Uforce.0000003600
> Uforce.0000007200
> 
> Finally, what do I set rbcsIter0 to?
> 
> Thanks for any help.  Feel free to ignore if there is no penalty to just making a single big forcing file.
> 
> Cheers,   Jody
> 
> 
> 
> 
> 
> --
> Jody Klymak    
> http://web.uvic.ca/~jklymak/
> 
> 
> 
> 
> 
> 
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