Ron Asher

The design of a similarity based deduplication system

We describe some of the design choices that were made during the development of a fast, scalable, inline, deduplication device. The systems design goals and how they were achieved are presented. This is the firs deduplication device that uses similarity matching. The paper provides the following original research contributions: we show how similarity signatures can serve in a deduplication scheme; a novel type of similarity signatures is presented and its advantages in the context of deduplication requirements are explained. It is also shown how to combine similarity matching schemes with byte by byte comparison or hash based identity schemes.

Similarity based deduplication with small data chunks

Large backup and restore systems may have a petabyte or more data in their repository. Such systems are often compressed by means of deduplication techniques, that partition the input text into chunks and store recurring chunks only once. One of the approaches is to use hashing methods to store fingerprints for each data chunk, detecting identical chunks with very low probability for collisions. As alternative, it has been suggested to use similarity instead of identity based searches, which allows the definition of much larger chunks. This implies that the data structure needed to store the fingerprints is much smaller, so that such a system may be more scalable than systems built on the first approach.This paper deals with an extension of the second approach to systems in which it is still preferred to use small chunks. We describe the design choices made during the development of what we call an approximate hash function, serving as the basic tool of the new suggested deduplication system and report on extensive tests performed on a variety of large input files.