Planned backup solution

After upgrading the main disk in my Mac Mini to a 320Gb hard drive, I also picked up an external USB Iomega disk of similar size. This was setup as a Time Machine disk to backup the system folders, but partitions to give me a Storage partition for my RAW files.

However, I have now reached the point where Time Machine is unable to back up due to not being big enough... In addition, none of my RAW files are currently backed up. So here's the plan:

1. Purchase external dual-drive enclosure with RAID support, and fit 2 x 3Tb hard drives. One disk will store the RAW files, the other will be setup as a mirror of the first.
2. Move RAW files from Storage partition to RAID drive using Lightroom (to retain metadata/developer settings).
3. Repartition Iomage disk to be a single Time Machine partition.

This should mean that I have the RAW files being backed up to the mirror disk, and the main system disk being incrementally backed up by Time Machine.

Does anyone see any issues with this setup before I take the plunge?

Thanks,
Paul