Hash value comparison during crash-tolerant incremental change tracking between backups of a source storage

A method of crash-tolerant incremental change tracking between backups of a source storage, the method comprising:

• assigning each block in a source storage into one of multiple zones, each of the zones including multiple of the blocks;
• creating, in a nonvolatile storage, a nonvolatile zone map that represents each of the zones;
• tracking, in the nonvolatile zone map, each of the zones that is changed between a first point in time and a second point in time, each of the zones being marked as changed in the nonvolatile zone map upon the first receipt of a request to write to any of the blocks of the zone and prior to execution of the write request;
• identifying, as potentially changed zone blocks, the blocks in the source storage assigned to any zone marked as changed in the nonvolatile zone map;
• identifying, as potentially outdated backup blocks, the most recently backed-up blocks in one or more prior backups of the source storage that correspond to the potentially changed zone blocks, the one or more prior backups representing the source storage at the first point in time;
• calculating source hash values of the potentially changed zone blocks;
• calculating backup hash values of the potentially outdated backup blocks;
• and
• subsequent to the second point in time, comparing the source hash values to the backup hash values to determine which blocks in the source storage actually changed between the first point in time and the second point in time.