Data size not consistent with its' true size

[marsipu (Martin Schulz)]

Hello @BarryLiu97,

I had a similar problem, when using raw.save() with my data:

FIF-File 2x disk-size after first loading

Dear MNE-People, when I first load Raw-Data into MNE-Python from a freshly generated FIF-File by our Neuromag122, the same unaltered Raw-Data takes 2x the space when saved to disk again. Does somebody has similar experience with their freshly generated data? I uploaded an example file with code here. Maybe there are some old FIFF-Data-Types in our data which get converted into larger types by default. Is this mandatory to work with MNE-Python or could one somehow avoid the doubling of disks…

It turned out, that the parameter fmt was crucial, as its default doubled my data in size. That could be solved with setting fmt=raw.orig_format.
Does this solve your problem too?