Not to be a downer, but you're pretty much wrong on this. RAID 1 is mirroring, and mirroring can be done at anytime whether you're using a hardware based mirroring (where the mirroring is totally seperate from the OS, so the OS only sees one drive and has no idea what it really there) or software based mirroring (for example how Windows does it)...in both cases I have yet to see a hardware RAID controller which will not let you build a mirror at anytime, once you attach the new drive you have to tell the RAID controller which drive to copy from/to but it will start the duplication process, which also is done in the background, you can reboot and whatnot and it affects it none since it's a whole nuther left below the OS...just as easy in Windows...haven't tried Linux but can't image it's tough...