Number 3 there is just… wrong. It shows selecting striped, bit striped is raid0, not 1, so if you selected that, that’s why. If you selected mirrored though you should indeed only see 20tb if each drive is 20. There should be no issue with having had storage spaces previously no.

Ok so, storage spaces isn’t the same as raid. A mirrored storage spaces pool, is not raid1. It’s very similar to it in that it’s a mirrored set, but it’s not the same thing. In a raid, because see, in storage spaces, you can have a mirrored set with 3 drives, and you’ll actually be able to about one and a half times one drive of data in that pool. This is because in storage spaces, it’s the DATA that is being duplicated, not the drives. So don’t confuse the concepts.

Now, as for why it shows that size, well, because you configured it to. Storage spaces completely decouple the pool size from actual currently usable space. You can create a pool of only 1 8gb drive, and yet say it’s a 1PB pool and it’ll happily do it for you. You’ll still only be able to actually store 8gb ofc, but the pool will report rhe 1PB of maximum space.

Generally the enclosures are just that, enclosures that offer the connection. There are exceptions though where enclosure does something more. Some enclosures do encryption and some just use the same controller for single drive and multidrive and your one drive is actually set up as a 1 drive raid array in which case you may have data slightly shifted to accomodate the headers for that. You can then still recreate everything, but it’s a pain.

But as I said, generally they’re just providing the drive as is in which case there won’t be any issue.