This is what I want to do,
1. Every Friday make two full backups (one backup to keep onsite and one to take offsite)
2. The rest of the week create differential backups
This is my concern; if I simply run the full backup job twice on Friday then the first run will reset the archive bit on all files. After the first run files may change and then the second run will reset the archive bit on all files. Then the next differential backup will search for files that have changed based on the archive bit. There is now a possibility that files which changed since the first full backup will not be included in the next differential backup (because there archive bit was reset by the second backup).
After reading around on the newsgroups and the manual, it looks like the best way to handle this is to backup up to disk and then create two tape duplicates from that disk backup. As I understand it there is no way to create a duplicate backup off of an existing tape to another tape if you have only one drive. Is this correct?
Any input, clever ideas, personal experience with the matter would be greatly appreciated. Thank you.