[CentOS] 4 X 500 gb drives - best software raid config for a backup server?

>
> If I have to do hardware raid, I'll definitely spec in a backup 
> controller. Learnt this the hard way when my raid 5 controller died 
> years after I first got it and I could no longer find a replacement.
>
> For high budget projects, having the extra raid controller as 
> insurance isn't a big deal. But for most budget setup and cost 
> conscious clients, soft raid obviates that hardware dependency.
You forgot flaky hardware. Boards that lose their configuration from 
time to time and what not...I heard stories about Mylex for example...