Thanks!
All drives will be plugged simultaneously and visible to the OS at the same time. If you want specifics, a LSI Logic SAS 9207-8i Storage Controller in HBA mode (no RAID).
Whether I use the same Pool or create a new one is kinda beside the point. The old drives will go away and the Pool mapped to the same drive letter so that it can continue life as a Plex Server.
In thinking about it, keeping the Pool active in it's current job is a higher priority than how fast it gets done. Of course, getting all 20.5 Tb files copied is priority #1.
I've got 2x12 drives - they will be replaced with 2x20. After all is said and done, the 12's will be repurposed on another PC.
Thanks again...