I am in charge of a new website in a niche industry that stores lots of data (10+ TB per client, growing to 2 or 3 clients soon). We are considering ordering about $5000 worth of 3TB drives (10 in a RAID 6 configuration and 10 for backup), which will give us approximately 24 TB of production storage. The data will be written once and remain unmodified for the lifetime of the website, so we only need to do a backup one time.
I understand basic RAID theory, however I am not experienced with it. My question is, does this sound like a good configuration? What potential problems could this setup cause?
Also, what is the best way to do a one-time backup? Have two RAID 6 arrays, one for offsite backup and one for production? Or should I backup the RAID 6 production array to a JBOD?
EDIT: The data server is running Windows 2008 Server x64.
EDIT 2: To reduce rebuild time, what would you think about using two RAID 5's instead of one RAID 6?