Standalone Kotlin app (not Android)
Developed in IntelliJ IDEA
Nothing fancy but might be useful for someone else based on my use case
I have a very large MP3 collection and have always shadowed it on two portable hard drives. First on a pair of 250GB drives, then a pair of 50GB drives, etc. Fast forward to recently when the collection (just under one terabyte) was shadowed onto a pair of 2TB SSD drives.
As a Microsoft 365 subscriber, I get 1 TB of OneDrive space as part of the subscription. So I've painstakingly uploaded the collection to there. Due to the wonkiness of syncing to/from One Drive, drive formatting issues, etc., I ended without full confidence that the most recent version of my collection was up in One Drive. But I did know that all the latest versions existed on one or the other of the two portable drives.
This simple but useful standalone Kotlin app allows you to specify, by editing the source code, two separate volumes to be compared. I'm on a Macbook Pro but wrote the original version of this app on Windows, so it should be trivial to adjust the path format accordingly.
My library exists in alphabetical folders, so the main function makes calls like this:
// pass logBandName = true as the second parameter to see progress in the log
if (!azFolderCompare("_Christmas")) return
if (!azFolderCompare("_Numeric")) return
if (!azFolderCompare("A")) return
if (!azFolderCompare("B")) return
If your volumes are basically synced, you might just run it on everything. The app will fix simple filename dispcrepancies that I have encountered (question marks in the file name, space in front of the .mp3 extension). This can be added to as necessary.
Other issues such as missing folders (band name, album name), count discrepancies, track count or name discrepancies will stop the processing and let you fix them. That was fine for me, as the processing (after the first time for each folder) is pretty quick, and once a folder is clean, I will comment it out and run only on the remaining folders. For my just under 1TB catalog, it only takes about 15 seconds to process everything and report that the two volumes match exactly. And the non-verbose log output looks like this:
Procssing folder _Christmas... Folder _Christmas has no unfixable errors in 77 bands Procssing folder _Numeric... Folder _Numeric has no unfixable errors in 22 bands Procssing folder A... Folder A has no unfixable errors in 233 bands Procssing folder B... Folder B has no unfixable errors in 314 bands Procssing folder C... Folder C has no unfixable errors in 235 bands Procssing folder D... Folder D has no unfixable errors in 242 bands Procssing folder E... Folder E has no unfixable errors in 121 bands Procssing folder F... Folder F has no unfixable errors in 114 bands etc...
Now that I know my volumes match, I'll just trust OneDrive to stay in sync with one SSD drive and return the other to be Time Machine backup drive.