It wouldn't necessarily be slow! There's this wonderful paper from Usenix OSDI 2014 [1] in which the authors present an eidetic system: "a computer system [sho

It wouldn't necessarily be slow! There's this wonderful paper from Usenix OSDI 2014 [1] in which the authors present an eidetic system: "a computer system [should] provide the ability to recall any past state that existed on the computer, and further, [should] be able to provide the lineage of any byte in a current or past state." They implemented and evaluated it, too: "Preliminary data from several weeks of continuous use [show that] storage requirements for 4 or more years of usage can be satisfied by adding a 4 TB hard drive to the system. Further, the performance overhead on almost all workloads we measured was under 8%." [1]: Devecsery, David, MIchael Chow, Xianzheng Dou, Jason Flinn, and Peter M. Chen. “Eidetic Systems.” In Proc. 11th USENIX Symposium on Operating Systems Design and Implementation (OSDI 14), 2014. https://www.usenix.org/conference/osdi14/technical-sessions/presentation/devecsery https://www.usenix.org/conference/osdi14/technical-sessions/...