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Systems & Data Center · Intermediate

Data Deduplication

A storage efficiency technique that eliminates duplicate data blocks or segments, storing only one copy and references to it.

Definition

Deduplication can be inline (before writing) or post-process, and file-, block- or variable-segment-based. It is very effective for VM images and backups. Windows Server, ONTAP, backup appliances and VDO implement it.

Example

A backup repository achieves a 12:1 reduction ratio because nightly full backups are mostly identical.

Exam tip

Deduplication ratios depend heavily on data; encrypted and already-compressed data deduplicate poorly.

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