Multithreaded support in 7za

According to -m (Set compression Method) switch # ZipMultiThread - 7ZIP manual & documentation, mt defaults to on, so there's no need to specify it at all.

However, 7zip's implementation of the DEFLATE algorithm doesn't support multi-threading!

As you have already discovered,

7za a archive.zip bigfile

only uses one core.

But .zip files compress every file individually. When compressing several files, the multi-threading option compresses one file per core at once.

Try it and you'll see that

7za a archive.zip bigfile1 ... bigfileN

will use all available N cores.

If you want to speed up the compression of a single file, you have two choices:

1. Split up bigfile in chunks.

2. Use a different compression algorithm.

   For example, 7zip's implementation of the BZip2 algorithm supports multi-threading.

   The syntax is:

   7za a -mm=BZip2 archive.zip bigfile
   

Also, the syntax error is caused by your attempt to use the LZM Algorithm for a .zip container. That's not possible.

The possible algorithms for .zip conatiners are DEFLATE(64), BZip2 and no compression.

If you want to use the LZM Algorithm, use a .7z container. This container also handles the following algorithms: PPMd, BZip2, DEFLATE, BCJ, BCJ2 and no compression.

This is an old question, and not the answer to the specific question, but an answer to the spirit of the question (Using all cores to compress a zip format)

pigz (parallel gzip with .zip option)

pigz -K -k archive.zip bigfile txt

This will give you a zip compatible file 7x faster for same compression level.

A quick comparisons of zip compatible and non-zip compressors using single and multiple cores.

wall times on i7-2600k to compress 1.0gb txt file on fedora 20

67s (120mb) 7za (zip,1 thread)
15s (141mb) 7za -mx=4 (zip,1 thread)
17s (132mb) zip (zip,1 thread)
 5s (131mb) pigz -K -k (zip,8 threads)
 9s (106mb) bsc (libbsc.com) (not zip,8 threads)
 5s (130mb) zhuff -c2 (not zip,8 threads)
 2s (149mb) zhuff (not zip,8 threads)

wall times to decompress

4.2s unzip -t
2.0s pigz -t
5.1s bsc d
0.5s zhuff -d