Does 7zip compression level affect decompression speed?

Question

I have a directory that I would like to password protect and encrypt. I am using PeaZip to do this using 7zip compression. I'd like to use the 7z like a directory and hard drive space is not a concern, so I have opted for the "Store" compression level, thinking that this would also lead the the fastest decompression time. But if I can make the files take up less space without impacting functionality and decompression time, than I would prefer this. How does 7zip's compression level affect decompression speed?

As a note, I will likely be editing files within the 7z and will be adding files to it over time.

Answer 1

As I recall, 7-Zip decompression takes about the same amount of processing regardless of compression level -- the difference is in how much memory is used during decompression (mainly due to the size of the dictionary). However, in the "store" case, there's no decompression to do at all, so that's obviously going to be significantly faster than any actual decompression case.

That said, if you mainly want an encrypted folder, you're probably better off using a TrueCrypt container, as archives are not designed for frequent updating. But if you insist on using 7-Zip, at least make sure to create a non-solid archive.

Answer 2

I have just conducted a test using a 4.2G ISO of a PS2 game and there is negligible difference in decompression times (and size too) between the default 7zip compression and ultra:

Default:

Size:       4411064320
Compressed: 3135355831
real    4m55.908s
user    3m46.838s
sys     0m5.811s

Ultra:

Size:       4411064320
Compressed: 3118958337  
real    4m57.601s
user    3m45.949s  
sys     0m6.265s

(Ultra settings used: -m0=lzma -mx=9 -mfb=64 -md=32m -ms=on)

Answer 3

The higher the compression level the longer it takes to decompress. Assuming 0 is none 1 is the lowest and 10 is the highest. Going from 0 to 1 will be barely noticeable, but every step after that will be more and more noticeable.

The larger the file will make it more noticeable.

You data set will compress differently that anyone else data set so you need to just test it and see what happens.

Answer 4

7-zip compression levels are explained on their Help file:

In your case, I would advise to use the Normal compression settings as it offers the best trade off between compression ratio and decompression speed. Specially as you said that space is not a problems.

You make test using different compression settings and see which yields the best compression/decompression ratio and speed for the kind of files you have.