Byung-Gon Chun Petros Maniatis Scott Shenker John Kubiatowicz Tiered Fault Tolerance for Long-Term Integrity. 267-282 2009 FAST http://www.usenix.org/events/fast09/tech/full_papers/chun/chun.pdf conf/fast/2009 db/conf/fast/fast2009.html#ChunMSK09