Embodiments are described for reducing memory usage and disk I/O's for reading and writing streams in a deduplication storage system. Generations of backups of a stream can be tracked for the stream. In the first generation (first backup), stream data is ingested, segmented, and written to disk without looking up a fingerprint of each segment, to save disk I/O's and memory. After the first generation, an amount of stream data processed is tracked, and at dynamically tunable increments of data processed, a fingerprint index lookup is performed to disk. The fingerprint index is read into memory and subsequent fingerprint lookups are preformed to cache, until a next dynamically tunable fingerprint lookup to disk. The dynamically tunable increment of processed data can be randomly reset.