1. A method for deduplication of snapshots data in a data storage by a processor, comprising: partitioning input snapshot data into input similarity units, the input similarity units each comprising an enclosure group of changed tracked blocks and the enclosure group having a size of at least 8 megabytes (MB); deduplicating an input similarity unit with a corresponding similarity unit of a previous snapshot; and examining a deduplication coverage subsequent to the deduplicating, by referring to whether a number of calculated deduplication digests matched between the input similarity unit and the corresponding similarity unit meets a deduplication threshold; wherein if the deduplication coverage threshold is not met, a similarity search is conducted and the input similarity unit is deduplicated with a found similarity unit residing in a similarity index.