Re: [Fwd: Re: netCDF file question]

Wei,

> > Were you able to successfully write large files?  If you can write
> > them successfully, then the library is OK and you should also be able
> > to read them.  If you can't write them successfully, what was the
> > error you got?
> 
> I am not sure if the file was successfully written. I can see the file
> got to the size that is bigger than 2 Gb - without the option, the model
> will not write a file that is that big. However, I cannot read it back,
> at least the complete fields inside it - that makes me wonder if it
> is written successfully. I will have to go back and check
> if it has problem writting the files. 

The actual size limit for large files is 2**31 or 214748364 bytes,
about 2.15 Gbytes, so the file would have to bigger than this to show
it was successful in writing a large file.

In case it helps, I've appended a small test program in C that writes
a 3 Gbyte netCDF file.  If it succeeds, it prints nothing, and you get
a file in the directory from which it was invoked that's larger than 3
Gbytes:

  -rw-r--r--   1 russ     ustaff   3000000096 May 11 08:11 big.nc

If it fails becasue it's linked with a library not compiled to support
large files or on a file system not configured to support large files,
it will print an error message something like:

  line 79 of lfs.c: Invalid argument

after creating a file near the limit in size:

  -rw-r--r--   1 russ     ustaff   2147475456 May 11 07:57 big.nc

You could try compiling this, linking it against the netCDF library on
bluesky, and letting us know if it gets an error or successfully
writes a 3 Gbyte file.

To test whether you can read such a file, you can try the "ncdump"
utility, compiled with the same netCDF library you are using, on the 3
Gbyte netCDF file big.nc.  If it succeeds, you will see something
like:

  $ /home/russ/netcdf/build/buddy64-cdf2/bin/ncdump -h big.nc
  netcdf big {
  dimensions:
          n = 1000000 ;
          r = UNLIMITED ; // (750 currently)
  variables:
          float x(r, n) ;
  }

If it fails, because the ncdump library was compiled without the flags
needed for large file support, you will get an error message,
something like:

  $ /local/bin/ncdump -h big.nc
  /local/bin/ncdump: big.nc: Value too large for defined data type

--Russ

#include <stdio.h>
#include <stdlib.h>
#include <netcdf.h>

void
check_err(const int stat, const int line, const char *file) {
    if (stat != NC_NOERR) {
           (void) fprintf(stderr, "line %d of %s: %s\n", line, file, 
nc_strerror(stat));
        exit(1);
    }
}

#define NFIXED 1000000
#define NRECS  750 /* 100 -> 400 MB, 500 -> 2GB, 750 -> 3GB */

int
main() {                        /* create big.nc */

   int  ncid;                   /* netCDF id */

   /* dimension ids */
   int n_dim;
   int r_dim;

   /* dimension lengths */
   size_t n_len = NFIXED;
   size_t r_len = NC_UNLIMITED;

   /* variable ids */
   int x_id;

   /* rank (number of dimensions) for each variable */
#  define RANK_x 2

   /* variable shapes */
   int x_dims[RANK_x];

   /* enter define mode */
   int stat = nc_create("big.nc", NC_CLOBBER, &ncid);
   check_err(stat,__LINE__,__FILE__);

   /* define dimensions */
   stat = nc_def_dim(ncid, "n", n_len, &n_dim);
   check_err(stat,__LINE__,__FILE__);
   stat = nc_def_dim(ncid, "r", r_len, &r_dim);
   check_err(stat,__LINE__,__FILE__);

   /* define variables */

   x_dims[0] = r_dim;
   x_dims[1] = n_dim;
   stat = nc_def_var(ncid, "x", NC_FLOAT, RANK_x, x_dims, &x_id);
   check_err(stat,__LINE__,__FILE__);

   /* leave define mode */
   stat = nc_enddef (ncid);
   check_err(stat,__LINE__,__FILE__);

   {                    /* store x */
    static size_t x_start[RANK_x];
    static size_t x_count[RANK_x];
    float x[NFIXED];
    int i;
    int r;

    r_len = NRECS;                      /* number of records of x data */
    
    for (i=0; i<NFIXED; i++) {
      x[i] = i;
    }    
    
    for (r = 0; r < NRECS; r++) {
      x_start[0] = r;
      x_start[1] = 0;
      x_count[0] = 1;
      x_count[1] = n_len;
      
      stat = nc_put_vara_float(ncid, x_id, x_start, x_count, x);
      check_err(stat,__LINE__,__FILE__);
    }
   }
   stat = nc_close(ncid);
   check_err(stat,__LINE__,__FILE__);
   return 0;
}