Deduplicating

Deduplicating, or deduplication, is the process of identifying and removing duplicate copies of data to reduce storage usage and improve efficiency. In a deduplicated system, only a single copy of repeated data is stored, with references kept for all instances that refer to that data block or file.

The technique relies on data identification and substitution. Data is divided into chunks or blocks, and each block is analyzed and hashed. When identical blocks are detected, duplicates are replaced by pointers to the single stored instance. Dedup can be implemented with fixed-size chunking or with content-defined chunking, which adapts to data changes to improve effectiveness and reduce fragmentation. It can operate at the byte, block, or file level, and is often complemented by integrity checksums to verify data.

Deduplication can be applied in different modes. Inline deduplication happens as data is written, saving space immediately, while post-process deduplication runs after data is stored. It may be used within a single system or across multiple systems, such as in backup solutions, archival storage, or cloud storage environments.

Benefits include reduced storage footprint, lower network bandwidth for backups and replication, and faster data movement. These advantages are especially pronounced in environments with many similar or repeated data, such as backups and virtual machine images. Tradeoffs include increased CPU and memory requirements, added metadata management, potential latency, and the possibility that encryption or highly diverse data reduces dedup gains. Ensuring data integrity and guarding against metadata corruption are important considerations.

Common use cases are enterprise backup and archival, virtualized environments, and storage systems that provide built-in dedup features.