Tape may have been gathering steam as the go-to platform for archiving. But how reliable is it really? If you go back to a tape 30 years later, what chance do you have of being able to access the data?
Brian Weick, Professor in the mechanical engineering department of the School of Engineering and Computer Science at the University of the Pacific, has devoted many years to investigating the reliability and durability of tape. In particular, he has been looking into the dimensional stability of digital magnetic tape.
“Tape undergoes dimensional changes when stored in a reel for long periods,” said Weick.
So how much do environmental factors such as temperature and humidity affect tape over time? Weick checked out how much stress and strain tape experiences over its life. Strain, he said, is the change in dimension compared to its original dimension. As part of his studies, he focused on the BaFe tape.
“BaFe is more dimensionally stable than earlier types of tape,” said Weick. “As well as good stability under heat, it also performs well in humid conditions.”
He subjected BeFe to conditions of heat, strain, stress and humidity that simulated 100 years of wear and tear. He concluded that the dimensional stability goals set for tape over the past decade have been met due to improvements in substrate, overall tape properties and characteristics.
“Based on testing, tapes are dimensionally stable for 30, 50 and even 100 years,” said Weick. “However, it is advisable that tapes are written, stored, and read under ambient temperatures and low humidity.”
But dimensional stability is only one aspect of tape reliability. A metric known as hard error rate is another way to compare storage media. While consumer SATA takes one hour to reach its hard error rate and enterprise SAS takes 55 hours, LTO-6 tape takes 473 hours, and IBM’s latest tape systems are said to take close to 300,000 hours.
The traditional measure of reliability is in terms of nines. 99.999% is 3 nines of reliability. The most expensive enterprise cloud tops out at 9 nines and tape has achieved 12 nines, said David Cerf, executive vice president of strategy and business development at Crossroads Systems.
Another big plus for tape is security. Disk and flash systems have to be locked down by many layers of security in order to prevent them from incursion and attack. While these same depth-in-depth provisions should not be relaxed, tape has the advantage of being offline.
“You can’t hack tape as its offline,” said Moore.
Testing and vendor claims are one thing. How is tape holding up under rigorous real-world conditions?
David Yu, Technology Architect at Brookhaven National Laboratory, has to deal with a doubling of the data under his charge every two years and expects to be looking after 20 PB by the end of this year. A ridiculous amount of information is being generated by the lab's work on its particle accelerator (which smashes subatomic particles into each other at near-light speeds).
The lab has eight tape libraries now and each can hold over 10,000 cartridges. To keep up with archiving demands, data is being written at 2.5 GB/sec.
“In 2014, we restored over 7 million files from tapes at rates as high as 8,000 files per hour,” said Yu. “But we have so much data now on each cartridge that it is now necessary to make an extra copy of each one as one lost tape or an error on a tape is a big disaster for our research.”
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