I am thinking of building a small media server using a new pc I just came across. I want/need about 1-2 tb of storage and was toying with the idea of some form of RAID but don't know which one. I lost a 500 gig hdd and all data on it. I dont want to go through that again. Thats were RAID comes in but I don't like the idea of needing 2-4tb so it can mirror. Now for the Questions
Once its up and running can I add more to it?
Should I use 2- 1tb drives or 4- 500gb drives?
Should I use Seagate Barracuda or WD Caviar?
And will a 80+ power supply and green drives make a difference. I dont want to be green But I have 4 kids and a wife that think light bulbs and tv's magically produce there own power.

ps: this will run some form of Linux just haven't decided which one yet.

Check out freenas.... http://freenas.org/freenas

Should have all the answers you are looking for.

If you dont mind spending a few bucks...Windows Home Server is basically idiot proof and offers selective mirroring of data as well as automated PC backups.

The number of drives you need is somewhat dependent on the type of array your planning on making.

As for software this is a nice little distro I recently stumbled across:

http://www.amahi.org/

well if you want redundancy but dont want to buy twice as many drives you can do RAID5, basically you need 1 more drive than the size of the array you build, so 4x500gb will give you 1.5tb storage

downside is if a drive fails you need to replace the drive before you can access your data, but you dont lose anything

as for drives, ive bought nothing but WD (caviar green) lately and they've all been great