On our call this Monday, one of the panelist mentioned the number of nines they guarantee for some of their archival storage services. What he was referring to was the number of decimal places that 99.99% extends out to for guaranteeing the uptime and durability of the content. Yesterday, Backblaze had a great blog post discussing how they arrive at some of these calculations for their storage service https://www.backblaze.com/
blog/cloud-storage-durability/ . Backblaze is another cloud storage provider and there are very transparent about their infrastructure and regularly posts about hard drive failure rates and other topics that are useful to folks like ourselves, who plan for digital stewardship of cultural heritage materials.
Digital Preservation Librarian
Penn State University Libraries