Incorrect parameter error when using 7-zip from the command line in Windows

I am running the following command:

7z.exe a -t7z -m9=LZMA2 test.7z test.txt

However, I get this error: System error:The parameter is incorrect. The error only occurs if I use the -m9=LZMA2 or -m9=LZMA switches. If I remove it, it works perfectly fine. What am I doing wrong?

I am executing the command from Windows XP, 7 and 2008.

1 Answer

I believe you're misinterpreting the meaning of the -m? switch...
-m9=lzma2 doesn't give you better compression than -m0=lzma2, that's the -mx switch.

Try this instead:

7za a -t7z -m0=lzma2 -mx=9 archive.7z files