If photography is your business, get a dedicated RAID server for your backups. It doesn't have to be hardware RAID-5 or 6, as we use software RAID-5 or 6 for a lot of mission critical stuff. If photography is your hobby, then RAID-1 should be good enough with 2 large HDs. It all depends on your requirements (speed, capacity, etc).
There are two points here that a few people have discussed:
1) data protection (RAID is the most common technology to address this); and
2) backups.
The two should not be confused.
There is no one-size-fits all storage solution - we all need to analyse our needs, and build a solution that fits.
What is important to remember is that RAID will protect you from a single hard drive failure (or two hard drive failures with RAID6 / RAID-DP - if you are using Netapp storage).
RAID will not protect you from a NAS or controller failure. To do that you need to look at solutions like replication (e.g. replicate data between two NASes).
RAID also does not protect against human error - i.e. accidental file deletion, or against operating system failure - e.g. your system crashes due to power loss, and the file system is trashed when you try to boot up again.
Try to consider all the failure modes you need to protect against, and then architect a storage solution that fits your needs.
For instance, RAID is not for everyone. You may find that individual hard drives are large enough, and that replicating between 2 NASes protects you from drive and controller failure, while backing up to the cloud protects you from finger trouble...
Overall that's the difference between a hobby and work. Clients don't want excuses, so you shell out for the battery backup modules hw RAID card, and you have a good UPS.
A journalling filesystem helps, and specially SGI XFS has a consistently high performance when dealing with series of large size files - it was developed by SGI for the visual effects workstations - all the compositing and post-production work was done on scanned 35mm film, which meant you ended up with imagine (the following is nothing abnormal), frame sequences of 5000 or 10000 16bpc TIFF files, or Kodak Cineon DPX files. Now mostly OpenEXR half-float, but still a very large number of frames of relatively the same size. Then you had to "record" the frame sequences into film again, but the all-digital workflow of today simplified that a lot. You still end up with vast sequences of large files for post-production and visual effects work, since that's the highend applications expect (mostly developed in-house, such as Nuke by the software department of Digital Domain, then marketed and sold, others not marketed at all, such as the compositor used by ILM, but they share an SGI IRIX ancestry, and porting them to Linux was relatively easy (and now some, such as Nuke, exist on OSX and Windows as well).
This just to point out that the choice of the file system is also a factor in the problem at hands. Some other filesystems, Reiser3 are great for very large series of small files, others are generalists, with average performance, such as Ext3 (i won't mention Ext2 since it doesn't has journalling), and there are other filesystems which record "snapshots" of the filesystem state at user-defined periods, i'm thinking mostly about Sun ZFS.
If the battery backup module of the hw RAID card, and UPS fail at the same time (unlikely), you still have the filesystem journal/snapshot, and for the most time you'll be able to savage the data without inconvenience. In some of these filesystems you might even place the filesystem journal/metadata in other hdds, mirrored, extra redundancy.
The backup plan, that's trickier and more expensive. Safe backups imply copies in different physical locations, tapes or hdds in fire proof vaults, and so on. There are companies that provide this type of service for critical data. It just depends what your definition of critical data is and how much you think it is worth. Granted this is overkill for the majority of people, but it's worth mentioning nevertheless.
I agree with your views, just wanted to add those details regarding filesystems.
