I have a server with three 500GB drives, with most of my data in a RAID5 configuration spanning the three of them.

I just purchased and installed four 1TB drives, and the intention is to move off of the old drives and onto the new ones. I have enough SATA ports and power connectors to power all seven of my drives at once, so I've kept the old RAID running while I figure out what to do with the new drives.

My question is: Should I create a whole new array on the 1TB drives, then move everything over and reconfigure linux to boot from the new md arrays? Or should I just expand the array, swapping out each of the three 500GBs with the 1TB, then adding the final drive?

I've read up on the mdadm extending drive setup, and it makes sense, but I imagine I would use one of the drives as a full backup while I move things over, then add that drive back into the array once things are up and running on three of the 1TB drives, so there's some complication in going that route as well... I'm just not sure which is safer/recommended.