For people who need greater digital image storage capacity than the current affordable 10.9TB Thecus then you may want to have a look at the following solution:
http://www.storagereview.com/synology_targets_photographers_new_ds2411_nas
I would estimate that filled with 3TB drives this should provide between 24-30TB of usable Raid 5 space (36TB unformatted). To put this in perspective thats enough for over 1/2 million uncompressed A3+ Tiffs or over 1 million camera raw images.
Synology have a good reputation for building solid kit so this look like a viable way to accommodate image collections. The 165mb/sec writing and 195mb/sec reading in raid 5 mode means that access to images is not going to be a problem.
As always – this is not a backup solution in itself, copies of all files must exist in some form as the device is a single point of failure (theft etc). What it does provide is fast and simple access to a large image collection.