Ask HN: Is it possible to reverse a disk recovery algorithm?
I created a software RAID from Drive A, added Drive B as a member and started it building.
In the morning, the RAID had failed. Drive B had complete data, but it was the original, older data. Drive A was unreadable, but functioning.
I wanted to get some SSD drives for managing my external backups anyway so I bought some. I couldn't get 4TB SSDs in the brand I wanted. The data on Drive B was less than 2TB, so I bought the 2TB SSDs, my intention was to speed up my backup process after having dealt with this issue.
I attempted to recover Drive A using Disk Drill to one of the 2TB SSDs, but it ran out of space. Evidently Drive A had contained quite a bit more than Drive B.
I copied Drive B to one of the 2TB SSDs, then I recovered Drive A using Disk Drill to Drive B.
The recovery "worked". I had 3 directories:
1) Deep Scan - HFS+
2) Reconstructed
3) Reconstructed labeled
The only file of note in Deep Scan - HFS+ was my Photos library (the most important thing really) and in the others were some older JPG/MPG directories that I had created before I started using Macs and/or Photos.
Those files were fine, I could preview them before recovery and I could see them on the new drive.
I was feeling a bit paranoid so I hastily copied this recovered data back to Drive A (at this point, I deleted the RAID from Drive A which gave me a warning about how it might work or it might lose everything, and it lost everything, and I reinitialised the drive, but remember I thought that I had a complete recovery).
It wasn't until I took one of these 2 drives (both now with the same content) and plugged it into a Mac running Photos that I realised I couldn't open the Photos library.
I went into the originals folder in the Photos library, and even though the files are all the correct size and have the correct names, they're not valid image files (I can see the difference if I open in vim between 2 files that were originally both on Drive A and Drive B -- it's all binary junk but in the original originals on Drive B, I can see Exif data and so on, in the "Recovered" files, I can't).
I looked at a couple of other recovered files that were just strangely named temp files or old text files, and they're also junk binary data.
So my question is:
Is it possible somehow to "reverse" the "algorithm" used by Disk Drill to recover the data in the first place? It seems all the data is there somehow, it's just encoded in such a way that I can no longer read it.
Disk Drill support have said "No, you can't do that" but I thought I'd ask here in case someone who knows more about how disk recovery works knows some way I could transcode and/or recover binary data either into the correct format OR back to an original disk image so I can re-run the recovery process (NB: Disk Drill support said that I might get a better result using Disk Drill 5 which is available only as a download from their website, not the Mac App Store, because it's hard to publish low level stuff on the Mac App Store and they can't get version 5 on there for ... reasons).