“The more copies, the safer. As the size of the data increases, the per-copy cost increases, reducing the number of backup copies that can be afforded.”
“The more independent the copies, the safer. As the size of the data increases, there are fewer affordable storage technologies. Thus, the number of copies in the same storage technology increases, decreasing the average level of independence.”
“The more frequently the copies are audited, the safer. As the size of the data increases, the time and cost needed for each audit to detect and repair damage increases, reducing their frequency.”
David S. H. Rosenthal, “Keeping Bits Safe: How Hard Can It Be?“ Communications of the ACM, November 2010.
The Story of Information 