The first commercial digital-tape storage system, IBM’s Model 726, could store about 1.1 megabytes on one reel of tape. Today, a modern tape cartridge can hold 15 terabytes. And a single robotic tape library can contain up to 278 petabytes of data. A tape cartridge simply sits quietly in a slot in a robotic library and doesn’t consume any power at all. Tape is also exceedingly reliable, with error rates that are four to five orders of magnitude lower than those of hard drives.
https://spectrum.ieee.org/computing/hardware/why-the-future-of-data-storage-is-still-magnetic-tape
The offline nature of tape also provides an additional line of defense against buggy software. For example, in 2011, a flaw in a software update caused Google to accidentally delete the saved email messages in about 40,000 Gmail accounts. That loss occurred despite there being several copies of the data stored on hard drives across multiple data centers. Fortunately, the data was also recorded on tape, and Google could eventually restore all the lost data from that backup.
ref : https://www-03.ibm.com/ibm/history/exhibits/701/701_1415bx26.html https://gmail.googleblog.com/2011/02/gmail-back-soon-for-everyone.html https://www.computerweekly.com/blog/StorageBuzz/Microsoft-revives-MAID-with-Pelican-but-tape-can-still-sleep-easy
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