IDL 8.1 { x86_64 darwin unix Mac OS X 8.1 Mar 9 2011 64 64} Mac OS X 10.7.3 I am trying to write a large data array to an HDF5 file using the IDL libraries, and it appears as though I can not write a dataset that is larger than 4.3GB. I can write multiple datasets to a file that add up to more than 4.3GB. I get an error at the H5D_WRITE proceedure with "H5D_WRITE: can't write data: Object ID:83886083" or some such number. More specifically, if I am writing out floats, I can not write more than 2ll^31/4-1. If writing doublefloat 2ll^31/8-1 Here is a test code: PRO Testhdf5file filename = 'test.hdf5' npoints = 2ll^31/8-1 ; This works ;npoints = 2ll^31/8 ; This does not work data = DINDGEN(npoints) file_id = H5F_CREATE(filename) datatype_id = H5T_IDL_CREATE(data) dataspace_id = H5S_CREATE_SIMPLE([npoints]) temp_ds_id = H5D_CREATE(file_id, 'Fake Data', datatype_id,dataspace_id) H5D_WRITE, temp_ds_id, data H5D_CLOSE, temp_ds_id H5F_CLOSE, file_id END