Save -v7.3 with large .mat files

I am trying to save large variables (5,000,000 x 200 arrays) to .mat files using save and -v7.3. Originally, it would save these files to be around 1gb which is manageable. After I made some small changes to the code that don't change the overall outputs, it saves the same files to be upwards of 20gb which is not manageable. How does matlab decide what file size to use? Obviously, it has the capacity to save these large variables to small files, but it suddenly decided to stop.

[Gargi Patil]

HI Michael,

Could you please share further details about your former and new implementation using the save function?

In particular, is there any change to the data structure of the variable being saved? The -v7.3 algorithm uses an HDF5 file format to save the data, which adds extra metadata to the file. The metadata can change the size of the file and is depenendent on how complicated the data structure is.