file size restrictions?

Dear all,

because I'm adapting HDF to an embedded system I also like to minimize the file size. Files generated with the HDFlib seems to have several locations with zero padded regions. To test this I generated a simple hdf file with HDFview with one compound consisting of a double and a float value. No value is placed into the content. After that I manipulated it step by step using a Hex-Editor. You find the result attached to this email. All contents are placed directly after another with no zero padding in-between.
Everything worked fine till I tried to remove the last 0x28 bytes in this file. For sure I always adapt the file size entry also (at offset 0x28). As soon as I do this the compound that is in the file is not visible anymore. The content of the last 0x28 bytes seems to be meaningless. I filled them with arbitrary values and still get a correct displayed file in HDFview. The same is true if I extend the file at the end. And So it seems to me there is a minimum file size depending on the content of the file.
Is there something like a file size minimum or an equation based on the several elements that are in the HDF file that leads to a minimum file size?

Best Regards

fsizecheck.h5 (680 Bytes)