Best Compression method?

[Nintonito]

I tried gcz but the compression ratio is generally close to 90% or higher, which isn't very effective. What are your thoughts? What compression method do you use?

[pauldacheez]

It all depends on the game. Animal Crossing, for example, can be compressed down to ~60 MB, while basically every two-disc GC game in my library still takes up at least 1 GB per disc. The disc that comes with the Game Boy Player even goes all the way down to 2 MB.

You can use GCMUtility to shave an .iso down before .gcz-ing it for a small gain in space savings (e.g. the post-GCMUtility Animal Crossing .iso is 32 MB, then .gcz'd it's 16 MB), but it's irreversible, it can break certain games that don't know how to disc reasonably, and the hashes will no longer match with redump.org's so you won't know if your dump was/is good or not unless you checked it beforehand or saved the original full-size .iso.

You can also do the same for Wii games (scrub/trim/etc.) via one of the numerous WBFS utilities. (I prefer the CLI-only wbfs_file utility since it's one of the few I don't need Wine for.) Again, it'll modify the .iso irreversibly which can break certain games and make dump verification impossible without the original file.

I personally recommend keeping the full-size originals (dumped fresh from disc and redump.org/GameTDB-verified) somewhere if you have the space for them, and only using compression if you have a situation where it's requisite, e.g. you play your games on a laptop with a small SSD.