Patent ID: 7620785

Claim:
A method comprising: (a) overwriting old first data in a data volume with new first data; (b) storing a copy of the old first data in a roll-back memory, wherein (b) occurs before (a); (c) storing a copy of the new first data in a roll-forward memory; (d) overwriting old second data in the data volume with new second data, wherein (d) occurs after (a); (e) storing a copy of the old second data in the roll-back memory, wherein (e) occurs before (d); (f) storing a copy of the new second data in the roll-forward memory; (g) overwriting the new second data in the data volume with a copy of the old second data from the roll-back memory, wherein (g) occurs after (d); (h) overwriting the new first data in the data volume with a copy of the old first data from the roll-back memory, wherein (h) occurs after (g); (i) overwriting the old first data in the data volume with a copy of the new first data stored in the roll-forward memory, wherein (i) occurs after (h); (j) overwriting the old second data in the data volume with a copy of the new second data from the roll-forward memory, wherein (j) occurs after (i) and (g).