I have been performing tape backups and restores since 1972 or so. Magnetic tape is known to have flaws, consequently the devices that use tape for storage incorporate redundancies into the data -- multi-bit ECC (Error Correcting Code). While I was in the Navy I used open-reel tapes; and they were periodically "certified" on a machine that cleaned and tested the tapes. Backups were done scrupulously, generations maintained -- dailies, weeklies, monthlies. The certified tapes always worked and I have never had a failure to restore using Exabyte 8 mm helical-scan tapes or the current Ultrium tapes. I *have* had restore failures at sites that did not use certification procedures and which used recording techniques lacking any kind of ECC.

For the sake of speed I use a 7 generation disk-to-disk backup using rsync as an auxiliary to tape backup. Rsync is amazingly fast and maintains what looks like 7 full backup sets but in fact uses just a little bit more than the space of one. Files that have not actually changed get "hard linked" rather than copied -- looks the same, restores the same as if it was a real copy, but of course is nearly instantaneous and uses no extra space.

Anything that must be restored from more than 7 days old comes from the tape library where the daily, weekly and monthly tapes are kept.

Online backups are vulnerable to worms, viruses and logic bombs, tapes locked in a safe -- with the write protect tab set -- are much more secure repositories of data.

The problem for deep history is the rapidly changing technology of *everything*. In 5 years from now, will I be able to read a 250 gb external disk drive, or an Ultrium tape? It is probably easier to "bring forward" disk-to-disk libraries. I have tapes from 5 years ago that I really have very little hope of reading -- QIC 80's, Travan, Iomega. However, before I discarded the QIC 80 computer and drive, I copied the tapes to CD-ROM; then I use digital signatures (PGP or MD5 checksums) to provide integrity assurance since the originals no longer exist.