US Patent 7979401 Time based file system for continuous data protection

Tokens corresponding to data units written to a rewritable file system are stored, where an ordering relationship is maintained among the tokens, where the ordering relationship is such that a first token corresponding to a first data unit is of a lesser numerical value in comparison to a second token corresponding to a second data unit, and where the first data unit is written at an earlier point in time in comparison to the second data unit. The rewritable file system is reverted to an indicated point in time based on the ordering relationship that is maintained among the stored tokens.