I personally use mirrored 2TB sata drives to store my data and I make backups to an RD1000 to take offsite as needed. This arrangement is sufficient in 99% of all cases, regardless of industry. Anything more is simply a level of incremental protection or, as it is in most cases, for time saving purposes, not disaster recovery purposes.
If you are only storing your images on a raid array of some sort, YOU DO NOT HAVE A BACKUP. RAID, in and of itself, is NOT a backup. It's simply a redudent storage medium that is designed to handle some level of hardware failure. It does not protect against corrupt files, ovewritten files, delete files or total disaster (fire at your home, flood, etc).
Likewise if you have multiple raid arrays and are mirroring them in some way, you still don't have a real backup. File corruption / delete / edits will still be pushed across those arrays and you still have no answer for disaster situations.
A single drive solution that is backed up regularly (after any major changes, nightly, etc) to something that is removed from that main location is more than sufficient for most peoples use and for most disaster situations. If you want to take the local protection up a notch, you get a raid array of some sort which will protect you against a single hardware failure. All this really does for you is prevent you from having to invest the time in retreiving your data from your real backup source. Most of the software's for these online services are designed to monitor for changes and backup when there are any. It happens real time. So using those along with a single or multiple drive solution at home is plenty. You can spend limitless amounts of money on disaster recovery solutions, but there is a point where spending only results in a fraction of a percentage point of difference. Common sense is your friend.
controller or array (backplane) failures rarely result in drive corruption anymore, especially if it's a mirror.
,