[gradsusr] Low level I/O error: read error on data file

[Jennifer M Adams]

The “Low level I/O error” message usually means your flat binary file is the wrong size. GrADS makes a calculation of where to offset the pointer — i.e. how many bytes deep into the file it needs to go to read the desired grid. If the file read command returns an error, you get the message that tells you how many bytes it was trying to read from the file (in this case 1144) and the offset it was using (in this case -2129859208, which isn’t right and looks like some kind of precision error).

The first thing you should do is make a calculation of what the file size should be:
xsize * ysize * zsize * tsize * esize * number-of-variables * 4 (bytes)
If your file has some z-varying variables and some non-z-varying variables of if your data is sequential this calculation is a little trickier, but you get the idea. If your file size doesn’t match, then figure out where you went wrong in describing the grid or in creating your file. If it does match, then the file may be corrputed somewhere. Try displaying one time step at a time and figure out which T index causes it to fail — if that T value is where the file size crosses the 2GB mark, then you probably have a precision issue. GrADS 2.0.2 should easily be able to read a big binary file, but it may depend on the system you’re using to read it.
—Jennifer


On Feb 1, 2016, at 7:50 AM, Anna Lukianova <romashe4ka04 at rambler.ru<mailto:romashe4ka04 at rambler.ru>> wrote:


Hi, everyone!

I have 2-D data file with a lot of records in time.

When I want to plot variables for the last records of time, I obtain such an error  :


Low level I/O error: read error on data file. Error reading 1144 bytes at location -2129859208/


Is this error linked to some file limits in GrADS (I have 2.0.2 version) ?


Thanks in advance, Lukianova Ann.

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--
Jennifer Miletta Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
George Mason University



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