I was thinking of buying a NAS for home-usage. I've never used a NAS or had HDDs set up in Raids. Before I commit myself to moving all my data to a NAS I need to find out how difficult it is to upgrade and replace the NAS' hard drives.

Suppose I set up a Raid 1 NAS with two 1TB hdds. At some point in the future I will use up all the space and will have to install two new 2TB hdds. Now I'll need to migrate the data from the old disks to the new ones. Will I have to hook up one of the old disks in a computer and copy all the data back in the NAS? Or can the migration be done using only the NAS?

I realize the answer to the question might depend on the NAS model. Being a simple for-home solution I was thinking of getting something along the lines of D-link's 323.