David,

RAID-type hard drive storage serves a purpose and is cost-effective if the data files stored are relatively small and frequent and fast access serves a function to how the data is used. For instance a stock photo agency would be accessing (hopefully) their library frequently and fast retrieval would be essential.

But for the individual photographer image file storage involves usually large file sizes and infrequent access and a leisurely access time to files is not a cost detriment. In addition the longevity of the media may be an issue, and a hard-drive based storage system may not be even close to archival. Most testing of the media is on the basis frequency of access before failure, not on what the longevity is in years of relatively dormant storage.

Finally for the individual photographer storing high resolution image archive files capable of making large prints, the cost per megabyte of a RAID system is not competitive and affordable I think to most photographers.

for longevity I use e gold dvd's but the drobo is a gread way to secure the vast majority of your dataand give you instant access