1. A method for reducing resource consumption of a similarity index in data deduplication by a processor, comprising: partitioning input snapshot data into changed tracked blocks; grouping the changed tracked blocks into enclosing similarity units; processing for deduplication similarity units that contain at least one input changed tracked block; representing in the similarity index only a latest generation of repository data, wherein a single latest entry is maintained for a representative value in the similarity index; applying implicit deletion in the similarity index such that a similarly index entry is not removed or overwritten until a change with associated data of the similarity index entry is detected; maintaining a subset of bytes of the representative value in a similarity index entry to reduce an input/output (I/O) load on the similarity index of the deduplication system; deduplicating a respective one of the similarity units with a corresponding similarity unit of a previous snapshot; and examining a deduplication coverage; wherein when a deduplication coverage threshold is not met, a similarity search is conducted and the respective one of the similarity units is deduplicated with a found similarity unit residing in the similarity index.