There was a discussion sometime ago about perhaps enabling pigz (parallel gzip) with Slicer. How to unset default 'compress' option during save - #7 by pieper
At the time, question was lack of a windows port. I see there is one:
@pieper would this help?
https://blog.kowalczyk.info/software/pigz-for-windows.html
It is a complicated topic. Such changes should happen at lower level, in ITK and there are plans for it, see https://discourse.itk.org/t/adding-parallel-compression-to-metaio/1835/15.
Unfortunately, for me it seems that the discussion does not seem to converge to a reasonable solution (see my comments there).
That’s unfortunate. Breaking the nrrd compatibility between itk and non-itk based programs would be a pretty bad idea.