The tapes are guaranteed for 30 years.

Most optical discs do not have any guarantees about lifetime and the worst of them may survive only a few years.

There have existed special quality optical discs with gold mirrors that were guaranteed for 100 years, but those are no longer produced and a single modern tape cartridge stores as much data as thousands of those discs.

There are several mechanisms of degradation of optical discs. If the plastic does not seal well enough the metallic mirror, the metal can become oxidized and transparent, so it no longer reflects enough of the laser light. This is why certain archival discs used gold mirrors, which cannot oxidize. The plastic resin may also degrade in various ways and cause disc deformation.

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AshamedCaptain 2 hours ago | parent [-]

Any guarantee made by manufacturer about data on tape longevity is irrelevant unless it is easy for user to create the storage conditions under which is warranted, and that is usually not cheap.

not hard to find stories about data on LTO tapes being unreadable after 5 years. The same as stories of data on even the worst CD-Rs being still readable after 30 years ( i can personaly attest to that).

	▲	adrian_b 2 hours ago \| parent [-]
		Some CD-Rs will certainly be readable after 30 years, but there have been plenty of bad CD-Rs that have become unreadable after less than 10 years. I had several hundred CD-Rs. Most of them were OK, especially the gold archival CD-Rs from Kodak, so I have migrated the data from them mostly to save space and improve access speed, not for them being too old. Nevertheless there have been a few that have gone bad, but I had duplicates for all of them, so I did not lose the data. Had I not been cautious, I would have lost some of the data. The main problem of optical discs is their much too low capacity in comparison with magnetic media. A small suitcase with tape cartridges contains as much data as a big cabinet full of the most dense optical discs.