#186 files larger than 100MB still compressed due to 7z -m0=lzma2 flag

[Flying Hawk]

In source code, line 930 of FolderSync.cpp
the comment says "turn off compression for files bigger than 100MB"

However, even with the flag -mx0, 7z would still compress the file because -m0=lzma2 is present
Simplest solution would be to remove the -m0=lzma2 flag, since 7z uses lzma2 by default anyway.

[Stefan Kueng]

lzma2 is not on by default, because that's the encryption algorithm to be used. lzma2 has nothing to do with compression but only with encryption.

[Flying Hawk]

Surely lzma2 refers to the compression algorithm.
It's on by default according to 7z documentation. Also consistent with the many tests I did
7z format only uses AES for encryption, no other choices

references:
https://sevenzip.osdn.jp/chm/cmdline/switches/method.htm#MethodID
https://sevenzip.osdn.jp/chm/cmdline/switches/method.htm#LZMA2
https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Markov_chain_algorithm

[Flying Hawk]

http://www.7-zip.org/7z.html
https://en.wikipedia.org/wiki/7z#Encryption

[Flying Hawk]

screenshot from 7zip GUI

[Flying Hawk]

With -m0=lzma2 and -mx0, files get compressed with effect of -mx1
Without -p"password", "-mx0 -m0=lzma2" and "-mx1" produces the exact same output.
Without -m0=lzma2, -mx0 functions properly without compression. Encryption still works with -p"password"
These are verifiable with tests, as I have done.

There's no option for encryption algorithm when using -t7z, because 7z format only supports AES

[Stefan Kueng]

Ups, sorry. My fault. I mixed lzma2 with sha2.

But still: according to the official docs (which you can find in c:\program files\z-zip\7-zip.chm when you install 7-zip), when passing -m, the '0'  means Copy mode (no compression).

[Flying Hawk]

That's okay

Yes, -mx0 works as "copy without compression" when -m0=lzma2 is not present.
But when -m0=lzma2 is present, -mx0 effectively becomes -mx1
"-mx0 -m0=lzma2" and "-mx1" produces the exact same output (without -p"password).

All I said above is backed up with tests I did, not just from reading documentation