I always forget how to do this and always end up battling Google trying to find the reference for it. This page is a really good reference of all the command line options for 7-Zip, but just for my purposes, here’s how to set the compression method:
-mx0 : No compression (copy mode)
-mx1 : Very low (fastest mode)
-mx3 : Fast compression mode
-mx5 : normal compression
-mx7 : maximum compression.
-mx9 : ultra compression.
Have you used anything but ultra?
Actually most of the time when I’m looking it up, I’m looking to do ‘no compression’ mode – for example, I regularly create archives of sets of files that are already well compressed and there’s nothing to be gained by trying to compress them further (I’m just trying to combine them into a single file for distribution purposes).
what’s the differences between “maximum” and ultra?
Not sure of the details, but Ultra is a higher level of compression. You’d need to test with both to see what the difference is in sheer compression ratio.