My first thought is to call IBM support, but since it's an x3650 M3 you may already be without support and hence asking here. You also don't state the OS in use...but since we are talking hardware RAID array I'll digress.
Obviously you know the option is there to backup the data, recreate the array, and restore. So here's what I would recommend:
- Backup the array
- Add the new drives while the server is on
- Open the Megaraid utility (in Windows there is a GUI, not sure in Linux, you can download the utility from IBM's support site if you don't already have it)
- Look for the ability/option in the array to add disks to the existing array and then the ability to expand the array. I haven't been in the utility in a few years so I don't remember where all the options are, but click on the existing array and look at the options/menus you get to choose from.
- If it works and allows you to do it...great. If it doesn't...then you aren't any worse off than you were before with the recreate and restore option.
I know that may sound like a weak answer overall...but trying to help you out without simply closing the question as "call the OEM and ask".