An incremental backup system that performs the following (not necessarily in the following order): (i) making a plurality of time-ordered journal entries; (ii) determining that a corruption condition exists; (iii) responsive to a corruption condition, constructing a first incremental mirror data set that reflects a backup data set and all journal entries up to a first corrupted journal entry which is the earliest in time journal entry, of the plurality of journal entries, that is a corrupted journal entry; (iv) responsive to a corruption condition, constructing a second incremental mirror data set that reflects the backup data set and all journal entries up to the first corrupted journal entry; and (v) checking for corruption in the first and second incremental mirror data sets to determine the latest uncorrupted version of the data set.