Not sure exactly. But Backblaze has been pretty transparent on their approach. Backblaze takes user data, splits it into 17 pieces, add 3 pieces of redundancy

Not sure exactly. But Backblaze has been pretty transparent on their approach. Backblaze takes user data, splits it into 17 pieces, add 3 pieces of redundancy, and split it across 20 racks. Backblaze has a tiered response system, my memory is something along the lines of 1 of 20 disks dying = schedule for replacement the next business day. The 2nd disk triggers a quicker/higher priority response. 3rd disk triggers pages and all hands on deck. Given that disks have a annual failure rate on the order of 1%, and losing the first disk has a chance of 1% * 1/365, if a second disk is 4 hours that 1% * 1/(3656), and a 3rd disk is 1%/(36524) you end up with lots of zeros: 0.01(1/365) 0.01 * 1/(3656) 0.01 * 1/(365*24) .00000000000000014281 That's just to remove the redundancy, you still need to lose another disk before data is lost. Sure there's other failure methods, including those that could take out an entire data center. I did find a statement saying that data stored in the US-West region would be stored in both Sacramento and Phoenix, but not sure if that means each B2 object uploaded would be in both.