Reverse range lookup on a unified logical map data structure of snapshots

A method for reverse range lookup in an ordered data structure of keys, wherein each key comprises a logical block address (LBA) and a snapshot identifier (ID) of one of one or more snapshots in a snapshot hierarchy, is provided. The keys in the ordered data structure are in an order from smallest to largest LBA, wherein in the order, keys having a same LBA are ordered from smallest to largest snapshot ID. The method includes determining a range of LBAs and traversing the ordered data structure in reverse order until a key is found that: has an LBA and a snapshot ID that is less than or equal to the last LBA and the largest snapshot ID, respectively. The method further includes adding an extent corresponding to the located key to an extent result list if the snapshot ID of the located key is not within a deny list.