If you already have a back up / mirror, why not just do raid 0 for speed (assuming you're pushing large files) or JBOD + your raid5 as a mirror?
Just curious, what's your set up?
I'm in the build process still.
Using the celeron that was recently on sale.
Perc 5 raid controller(2TB limit
Either CentOS or Windows 7.
Currently I have two 2TB WD Reds. They'll be in a Raid 1 initially. As I get more, I'll convert to a Raid 5.
This will be a NAS, FTP, Torrent and VPN server. So Raid 0 doesn't make much sense. The OS will be on an SSD. If Anything, I could just get one of these and leave it external and set it to backup only important directories.
Oh the decisions.