If you look at all RAID implementations that exist, you're going to find exceptions. However, all the modern consumer varieties tend to have some things in common (by default). I'll stick to describing those. When you add a disk to a RAID array, metadata is stored at the end of the disk. It records the array the disk is part of, which other disks are in the array, etc. This is called the RAID superblock. If you create a RAID 1 array, your operating system will see them all as a single disk that is very slightly smaller than a single disk (due to the superblock). Everything you write to the RAID disk gets written identically to each of its member disks by the storage controller. Technically, disks are read/written in blocks (each block is multiple sectors in size), but this is all transparent to the user. Every file you create or change or delete is created/changed/deleted on every member disk simultaneously. This is true whether you have 2 disks in the array or more than 2.  If one disk completely fails, you can still operate just fine off the remaining disk(s) (but see the caution below). If you remove one disk and attach it to another PC, it should work fine. The partition information and everything is all at the front of the disk, just as expected. The superblock will just appear as some extra junk at the very end of the disk, outside any partition. In some scenarios, where it is recognized as a RAID member disk from another PC, there might be an extra step before it will let you use it, but it's all very doable. Caution:  Blocks are read from the disks in a staggered fashion. For example, with 2 disks, all the odd blocks are read from one disk and all the even blocks are read from the other. By working together like this, read speeds can be practically doubled. But this comes with a huge drawback. If a disk doesn't fail completely, but instead develops bad sectors, you may not realize it. The bad sectors may happen to be in blocks that are never read on that disk. In some cases, people have had bad sectors develop on one disk, then had the other disk fail, and only then realized that the remaining disk has bad sectors and corrupt data. Every backup method has its pros and cons. Never trust just RAID, or just an external HDD, or just the cloud. Use multiple methods to backup important data.

Evidence that it affects "most" people negatively? Based on what? The fact that their are millions of users in fact show me the opposite, that "most" are quite happy.

Raycast ftw.