TS-251 both drives failed, trying to get data onto new drive without possibility for backup inbetween

A while ago, one of the two 4TB drives I had installed started to report bad blocks but I didn't notice the lights as it was physically in another place and I hadn't logged into it in a while. Then the second one did the same, became read only and a short while after and then the system wouldn't even boot anymore.

Now I took out the old drives, put in a new 10TB one and started setting it up. I have not configured any volumes or storage pools yet. Now my question is what will happen, if I put one of the old ones back in to copy over the data. I honestly can't quite remember since it's been a while, but I think the 4TB ones were mirrored and should be copies of each other.

My question: Will LTS just start formatting as soon as it detects the drive, when I hotswap it in? Or do I get the choice of what should happen to it?

The thing is that I don't have another way of copying anything over, as I don't have any other large storage devices and can't connect the drives themselves to my laptop of course.