Wii disc internal hash checksums

[themanuel]

I was reading through this month's progress report and saw the bit about Wii disc MD5 checksum changing after scrubbing.  Now a warning has been added so that users know this. 

However, while the checksum of the image itself will change when removing the padding data, Wii discs have an internal checksum record that can be used to assess the integrity of the useful data, even after trimming the image.  This is used by Wii Backup Manager and other tools to verify images compressed or not.

Does dolphin use this feature when verifying checksums?

I don't think the Gamecube discs have this feature, so compressing those does permanently prevent their integrity being verified after being compressed.  Does anybody know?

[ExtremeDude2]

Isn't that for what is should be not what it is?

[JosJuice]

Wii discs have an internal checksum record that can be used to assess the integrity of the useful data, even after trimming the image.  This is used by Wii Backup Manager and other tools to verify images compressed or not.

Does dolphin use this feature when verifying checksums?

Dolphin is currently not using these checksums for anything. It's a good idea, though.

EDIT: Er, actually, I forgot that we have a function that uses them to verify the integrity of a partition. It's accessed by right-clicking a partition in the file system view in the game properties. I don't know if it interacts well with discs that have had blocks scrubbed inside partitions.

I don't think the Gamecube discs have this feature, so compressing those does permanently prevent their integrity being verified after being compressed.

Yes, except Dolphin does not scrub GameCube discs while compressing them, so they will still have the same hash.

[themanuel]

ExtremeDude2:

I did not quite understand your comment.

My guess is that dolphin uses the internal checksum feature when verifying the useful content of Wii discs but the message is just there to warn users that their original image will not keep its original checksum.

[themanuel]

Wii discs have an internal checksum record that can be used to assess the integrity of the useful data, even after trimming the image.  This is used by Wii Backup Manager and other tools to verify images compressed or not.

Does dolphin use this feature when verifying checksums?

Dolphin is currently not using these checksums for anything. It's a good idea, though.

EDIT: Er, actually, I forgot that we have a function that verifies the integrity of a partition. I think it's accessed by right-clicking a partition in the file system view in the game properties. It might not interact well with discs that have had blocks scrubbed inside partitions.

I don't think the Gamecube discs have this feature, so compressing those does permanently prevent their integrity being verified after being compressed.

Yes, except Dolphin does not scrub GameCube discs while compressing them, so they will still have the same hash.

Those internal Wii checksums would be useful to help validate bug reports.

Good point about the GCN disc compression. I should compress my images without fear of losing the hash and save myself some space.

[Jack Frost]

Main point about the hashes mentioned in the Progress Report is that you can verify them against known good hashes (such as http://redump.org/) or simply against what CleanRip/your-ripping-tool said in the end to see if your image has been transferred correctly. It does not refer to the integrity checks that might be built into the file system itself - altho we do seem to have both available for Wii disks.

[themanuel]

Main point about the hashes mentioned in the Progress Report is that you can verify them against known good hashes (such as http://redump.org/) or simply against what CleanRip/your-ripping-tool said in the end to see if your image has been transferred correctly. It does not refer to the integrity checks that might be built into the file system itself - altho we do seem to have both available for Wii disks.

Makes sense.  I'll have to play a bit with dolphin's image tools.  All of my ripping had been image manipulation in the past was done with the Wii and PC-based tools like WBM.

[mbc07]

From my experience with Dolphin's GCZ compression:

• GameCube to GCZ compression is lossless. Same MD5 of the original ISO after decompressing the GCZ file.
  
• Wii to GCZ compression is somewhat lossy. The files inside the ISO will remain intact, but the unused spaces will be scrubbed.
  

In other words, if your Wii ISO had the MD5 of a good dump before compressing it to GCZ, don't worry, its MD5 won't match anymore after decompressing but the game files will still be intact (you can confirm this by right clicking a partition and choosing "Check partition integrity" through Dolphin's Game Properties).
And about comparing the MD5 of a plain ISO vs a compressed ISO, as long as you use recent development builds (and use Dolphin's built-in "calculate MD5 hash"), Dolphin should return the MD5 of the uncompressed ISO, independent of whether it's compressed or not.