Hacking Question Difficulty shrinking NAND size with compression

cleeezzz · Dec 9, 2018

I backed up my switch on 4.1.0 many months ago and it compressed to about 10GB. I was attempting to shrink it by using HacDiscMount (following a similar route to Raj's updating without burning fuses guide) to delete my user content and system. I realized that I had to wipe each partition as well since the data does not get zero'd out (leading to good compression). I have tried using windows format (slow, not quick format) and used HxD to examine the USER and SYSTEM partition, they both seem fully zero'd out except the headers that windows adds for formatting. Doing a compression at this point was even worse than before, I could not finish the actual compression since I ran out of hard drive space but it was way larger than expected since it should be fully wiped, (expecting 500mb from other reports). When I examine the whole rawnand.bin with HxD, it is filled with data and only a small portion of it is zero'd out which is odd since USER is the biggest partition and it was confirmed to be zero when it was mounted. What am I doing wrong?

aut0mat3d · Dec 10, 2018

Nothing.
Content on NAND is encrypted, and when Horizon OS writes Files they will take Space.
Deleting Files will let the encrypted Sectors stay on the Filesystem marked as free, but encrypted nowadays which let
your compressed Backup grow...

shchmue · Dec 10, 2018

cleeezzz said:
I backed up my switch on 4.1.0 many months ago and it compressed to about 10GB. I was attempting to shrink it by using HacDiscMount (following a similar route to Raj's updating without burning fuses guide) to delete my user content and system. I realized that I had to wipe each partition as well since the data does not get zero'd out (leading to good compression). I have tried using windows format (slow, not quick format) and used HxD to examine the USER and SYSTEM partition, they both seem fully zero'd out except the headers that windows adds for formatting. Doing a compression at this point was even worse than before, I could not finish the actual compression since I ran out of hard drive space but it was way larger than expected since it should be fully wiped, (expecting 500mb from other reports). When I examine the whole rawnand.bin with HxD, it is filled with data and only a small portion of it is zero'd out which is odd since USER is the biggest partition and it was confirmed to be zero when it was mounted. What am I doing wrong?

you're writing zeroes unencrypted. only a small portion was zeroes because only small nand areas are unencrypted.

cleeezzz · Dec 11, 2018

Yeah, I found this comment on Reddit. My backup compressed to 310mb now, I will test if the backup boots tomorrow.

Step 0: THIS COULD CORRUPT YOUR BACKUP IF SOMETHING GOES WRONG, MAKE SURE YOU HAVE AT LEAST PRODINFO, BOOT0 AND YOUR GAME SAVES. I am not an expert, so your run this guide at YOUR OWN RISK!
Step 1: Dump all your BIS keys with biskeydump and save them somewhere safe. You will need them.
Step 2: Open your nand backup in hacdiskmount.
Step 3: Double-click on the user partition and input your bis keys, test and save them.
Step 4: Mount the User partition after you input the keys. Copy all the files inside to a folder.
Step 5: Copy everything into a folder. It should not take too much space, as all games should be deleted.
Step 6: Unmount the disk and remove your bis keys.
Step 7: Mount the disk without the BIS keys, do a full format or diskpart clean all
Step 8: Put the BIS keys back, DO NOT CLICK TEST, and mount it again and do QUICK FORMAT, fat32 16k allocation size, and put your files back. Unmount.
Step 9: Zip the backup and it should compress much better.

shchmue · Dec 11, 2018

ya that's the way

cleeezzz · Dec 12, 2018

For anyone who finds this thread later, I have confirmed that the backup boots, it gets stuck on black screen after Nintendo logo but I remembered that you MUST boot initially with the specifically modified hekate_ipl found in raj's updating firmware without burning fuses guide.

LegendOfAB · Jan 8, 2019

cleeezzz said:
it gets stuck on black screen after Nintendo logo but I remembered that you MUST boot initially with the specifically modified hekate_ipl found in raj's updating firmware without burning fuses guide.

Does anyone know why this is and if it is still required?

Hacking Question Difficulty shrinking NAND size with compression

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