@trurl, thanks a lot for quick replies! 😊
Oh, Ok... I see what you mean. Meh, I should have asked before doing anything, mea culpa 😔
I briefly thought about this approach but the word "rebuild" sounded a bit scary. I guess I should trust Unraid and go this path so I can experience what the process of replacing a drive and rebuilding it is. One of the best Unraid features, in fact the one I love most about it, is that even if I remove the 8TB drive, it will still contain an accessible copy of all its data, so if the rebuild fails, I should still have a working "backup".
I will follow your advice. If I understood everything correctly, these are the steps required to swap both drives:
1. Stop the array
2. New config removing the two 18TB drives and the 14TB drive (all three still empty at the moment)
3. Start the array and rebuild parity
4. Stop the array
5. Replace Data Drive 1 (8TB) with one of the 18TB drives
6. Start the array and let it rebuild everything
7. Stop the array
8. Replace the Data Drive 2 (8TB) with the second 18TB drive
9. Start the array and let it rebuild everything
10. Stop the array
11. Add the remaining 14TB drive to the Array
12. Start the array
On one hand, I'm thinking that at this point I can just remove the two 18TB drives, leave the 14TB drive, New config with Parity 18TB + original 8TB drives + already installed 14TB, then replace the 8TB drives from there. Steps 11 and 12 would not be needed. I'm also not sure if I have to rebuild parity at any other point besides Step 3 (for example, after a drive is rebuilt, though parity at that point shouldn't need to be rebuilt).
Do I need to preclear the 18TB drives again ("Clear Disk") or at least do some kind of verification ("Verify Signature" or "Verify Disk") before using them to replace the 8TB drives?
One of my doubts was if content could be copied between drives (via /mnt/diskX) with the array stopped, according to your comment it has to be done while the array is started, so it makes sense that parity must be updated.
That's one of the things that puzzles me... Is it ok to have duplicate data between disks while the array is running?? It's the reason why I thought that the array had to be stopped to copy data between data drives. I'm assuming that you "remove" the data from those drives when they are unassigned from the array or you physically remove them from the system, is that right? Unraid will automatically "see" the old data in the new drive.