potential cause for "Low Level I/O Error"

[Ryo Furue]

Hi Jim,

| Low Level I/O Error:  Seek error on data file
|   Data file name =
| /disk/c2/ofes/Tropical_Pacific/hbudget/post_4601/source.dta
| 657 rc=-1 pos=536871600 pfi->fhdr =0
| Segmentation fault

This error may be because that your GrADS cannot handle files larger
than 2GB. "pos=536871600", if interpreted as the number of 4-byte
reals, is just beyond 2GB.

| a single variable with (x,y,z,t) dimensions of 3600x420x54x31 and I
| get the error when trying to access beyond time=7, level=32, y=32.

Also, the 7th timestep is just beyond 2BG:

    3600 * 420 * 54 * 7 * 4bytes =~ 2GB

| A little more information for you.  First, the file size is correct,
| 10124352000 bytes.
| Second, I can read the first six time steps of this file, and then more
| than half-way
| through the seventh before I get the seg fault.  What is curious to me
| is that when I
| read the data via a fortran program, it all looks okay.  If I then
| simply write it to a
| new file, grads can read it without problem.  Finally, I can
| successfully read the data
| using both grads-1.9b4 and grads-2.0.a1, but I get the seg fault only
| when using
| grads-1.9.0-rc1.

So, I suspect that your old GrADS uses old system calls that can
handle only "small files" whereas newer ones support "large files".

Ryo