Ugh!!! I hate computers. TL;DR If you hate Mac, skip this.
I'm writing partly to vent, partly to get my head straight about how to approach the problem, and partly to see if others think I'm making it worse. This post was so long, that I had to delete half of it and it's still too long.
Basically, my 7 year old iMac 27" (4-core i5, 32GB RAM, 2TB SSD) was randomly ejecting my 8TB USB 3.0 RAID-0 drive, filled almost full with 20 years of iTunes Music and TV, CD rips the kids supplied, their downloaded MP3's, and ripped DVDs. It's on Mac OS Monterey from 2021, the latest Mac OS version that it's "allowed" to run on a machine that old, even though it's pretty speedy with that much RAM and SSD.
I had been doing incremental backups of the iTunes drive to a 12TB Synology NAS and Drobo 5N NAS. I also had an off-site copy of my media split across a 6TB and 4TB drive, from early last summer. With the random USB drive ejections, I'd have to do a disk repair on the ejected drives every time I rebooted to remount the drive. Sometimes the USB ejection issue also killed the BT connection to the keyboard and mouse, prevented using USB keyboard and mouse, and we'd have for force power down the Mac to get it running again.
I decided in the middle of December to make my 12 TB Synology NAS drive the primary media library drive since it was not being randomly ejected and causing file corruption. I would later use the USB 3.0 RAID as the incremental backup drive when needed. I did not know that Mac OS likes its drives to be non case-sensitive, and that my 12TB Synology NAS and my 32TB Drobo 5N NAS were both case-sensitive.
Once I started using the NAS drives for my iTunes Music and TV library, I could not back up my library to the non-case sensitive RAID drive to use it as my primary drive on the new MacBook Pro. The Music and TV apps had re-indexed and re-named my files with different upper and lowercase, according to how they were spelled in the app. It did not keep them merged into the same folder if the spelling was different by a capital letter here or there (i.e. "Sleep Through the Static" vs "Sleep Through The Static"}.
I found out when I went to do an incremental backup of the NAS back onto the USB 3.0 RAID drive, and the backup failed due to file name conflicts. Apple Music and TV seems to be doing fine with the data as is on the case-sensitive drive. I can just never copy a large portion of it to the internal non case-sensitive drive in one fell swoop if I someday get a larger internal drive.
Anyway, I tried going back to using the old non case-sensitive 8TB RAID as primary library drive, and I re-download all the new music and movies that I'd bought in the last 6 weeks. That would be MUCH EASIER than slugging through 27K songs looking for conflicts, right? Nope.
Apparently the incremental backup that failed has also REMOVED 25% of the files (2TB) that were previously on the USB 3.0 RAID drive, due to naming conflicts! Instead of leaving the old files in place they were just GONE. Not only that, but if I'd click on a link to play a song, sometimes it would play the wrong song, as Apple Music had indexed the files so that a song in the music database was sometimes linked to some other random song in the library!
The data on my old USB 3.0 RAID drive is basically toast, while the only problem with the data on either NAS is the mixing of upper and lowercase letters in a large number of the music files, especially if some of an artists music was a mix of manually added MP3s and purchased AAC files. That happened a lot over 20+ years.
I said screw it and wiped the 8TB RAID, re-formatted it as case-sensitive, and spent 2 days cloning the 7.92 TB of media from the NAS onto the 8TB USB RAID-0 again. When I started with the Synology NAS on the 1Gbit network and it was going to take 176 hours to copy almost 8TB, at 45GB copied every hour. I moved the NAS off the network, used a red crossover ethernet cable and DHCP to directly connect it to the iMac, and got it to copy much faster, running anywhere from 40-100 MBps. It still took about 50 hours, with about 160GB copied every hour on average. It felt like the good old USB 2.0 days.
(1) So, I can now use any of the 8TB RAID, the Synology NAS, or Drobo NAS as my primary data drive, and backup back and forth from one to the other without conflicts, since they're all case-sensitive; but I can not use a non case-sensitive drive to back up my 8TB of Music and Movies, due to the numerous file name conflicts. Mac OS itself only runs on non case-sensitive drives, so I can't just drag all my music back onto the internal drive again.
However, I will drag my music over from the off-site non case-sensitive backup drives to the internal drive, once I free up some space or get a new Mac with more storage.
(2) Another option is to get another large drive, like 16GB since the 8TB is almost full, format it as non case-sensitive as Mac prefers, restore the old 6TB+4TB off-site backup data onto it with Carbon Copy Cloner, then re-download 6-8 months worth of Apple music and movies purchases (300-400GB).
That way I'll have my full library back to a non case-sensitive drive as Mac prefers, and my library will be compatible with placing 27,000 songs back on my internal drive someday, once I get a new upgraded computer (next month). As long as I don't actually run Apple Music or Apple TV apps directly from the NAS copies, the music and movie files wont get renamed with conflicts, and they can still be restored to a non case-sensitive drive in the event of a primary drive failure or data loss.