I currently have Ubuntu Server 13.10 (upgraded from 12.10) installed on an old Dell PC at home. When I set it up, I tossed in 2 1TB drives, and set up raid0 to simplify using all their space. I know this is basically awful, but it's a media/file server with lots of files that are either backed up elsewhere or easy to replace.
Anyway, 2TB is approaching being insufficient, and raid0 has me reasonably uncomfortable about the reliability of the system. Although important files are backed up, we've hacked together enough stuff on it in an undocumented way (again, awful, I know) that it'd at very least be unfortunate to lose the system/program/config files. So I'm getting a new 4TB drive to replace both. Ideally, I'd like to also eventually slot in a second 4TB drive and set up raid1, when I can afford it, but that's a secondary goal.
However, the PC only has two ports for drives. I also currently do not have any other single drive with sufficient capacity to copy the entire 2TB to intermediately. What is the best way, if any, to transfer my installation to the 4TB drive? Uptime isn't important, just being able to replace the two drives with one larger one while minimizing other system changes.