Multiple drive sets with PR4100

With the 10TB Red drives being on sale right now, I’m looking to upgrade the storage in my PR4100 from the 6TB drives in it now to 10s. I’d also be wanting to take the opportunity to encrypt the volume, since I missed doing that during the initial setup, so I can’t just do multiple RAID rebuilds and an expansion. I don’t have enough storage space elsewhere to offload the ~16TB of data I currently have on there. Has anyone ever switched back and forth between multiple sets of drives on the PR4100?

I do have an unused 4TB drive sitting around, so my plan would be to transfer 4TB of data from the existing array to that, shut down the NAS, swap in the 10TB drives, transfer the 4TB to them, shut down, swap back to the 6TB drives, and repeat until all 16TB have been transferred to the new array. I’m just worried that some configuration will be lost when swapping back and forth and that I might lose everything. Has anyone ever tried something like this?

I’m specifically not wanting to do this with expansion/rebuild. I want to be able to switch between the current 18TB (4x6TB in RAID5) and the new 30TB (4x10TB in RAID5) in the same NAS by physically swapping all 4 drives at the same time. I just don’t know how the stored configuration on the NAS will handle that. I need a way to transfer all the existing data to the new array, and after dropping over $800 on new drives the “toys” fund is depleted and getting a couple more drives isn’t in the cards for a while. If I have to, I’ll put together a Linux PC from spare parts and load the 6TB drives and see if I can get it to mount the array with mdadm and just transfer from that, but not having to do that would be preferable.

I understand what you’re saying that it’s dangerous to swap each drive one at a time since it causes a rebuild each time you do that, which puts a lot of strain on all the drives. That’s not what I’m talking about doing. I want to shut down the NAS, remove all 4 existing drives, and insert 4 new drives, and create a fresh new array on those new drives. I then want to go back and forth between the two configurations, using a completely separate drive to transfer files a few TB at a time between them. At no point would this trigger a rebuild since the arrays will always be intact, there will just be two of them.