[feznuk]

Since you already have 900GB of data to deal with I’d buy the additional drive and build the 3-disk raid5 volume with the three new drives. Then you can copy over the data to the new volume.

Remember, there’s a cost for fault tolerance. With three disks you’re going to lose about 1/3 of the total capacity. Your resulting raid5 volume will only be ~2TB.

When finished you’ll have:
- One ~2TB raid5 volume.
- One 1TB non-raid disk.

As far as setting up the array…you should see your raid controller post during bios. You’ll see a banner post with the name of the maker of the chipset (for example, LSI). You usually get some basic information then the controller searches for disks. At some point you’ll be asked to hit Ctrl-H, Ctrl-M (or something similar) to enter the setup utility. That’s where you’ll set up the array.

FYI…you can’t just add a disk to a raid array to change the raid type or number of disks in the array.