I want to create a long-term data archive of old stuff I don't need daily, but don't want to throw away either (e.g. all raw data of my thesis work). Optical media have failed me too often in the past, so now I am using an external USB disk and - to protect against accidental modification of the archive - I create ISO images of data batches and store these (and mount them on demand). The harddisk is NTFS formatted for portability (read/write for Linux and Windows, and at least readable for Macs).
My question is: Are ISO images on external harddisks a good idea for long-term archiving data? How about bad disk sectors? It sure sounds easier for the OS to fsck a disk with 200 ISO images instead of 2,000,000 separate files, but is it? Should bad disk sectors be my primary worry when thinking about long term archives?
Any ideas - or alternatives - for an affordable long-term data storage concept would be appreciated.