I currently have only two external USB2 drives (80 and 160GB) - my intention is to add 2+ more (200+GB) in a rotation. These may go off-site. However I'd like to also have immediate on-site from the prior day. My online storage is around 100GB. Estimated changes are 5-10GB per day. I want to do daily incremental or differential backups using TI to an external USB drive. I also want to be able to take a drive off-site as needed. Would it be best to do physical copies of the on-line TI backups periodically? Or is there another way to make sure that each off-site copy contains all of the files necessary to do a restore to that point-in-time?