If its home network
I bought 2 of these www.maplin.co.uk/Module.aspx?ModuleNo=97390

I use this program www.han-soft.com/habt.php (Auto backup freeware)

Plug them into the router and you have cheap wireless backups
( Gooch Is neither here nor there, Mon 15 Jun 2009, 13:37, archived)

They are not raided
But just set the backup to do the same thing to each disc
( Gooch Is neither here nor there, Mon 15 Jun 2009, 13:41, archived)

That would involve having at least 5 of those boxes.
The best I found so far is an external RAID box that holds 2 drives. Might go for those.
( Dave Trouser ; the people's choice - 75% agree, Mon 15 Jun 2009, 13:43, archived)