Backup Rotation Storage Calculator

Method and input definitions

Uncompressed repository = full-copy size × full-copy count + changed-data-per-day × incremental-retention days. Estimated stored size = repository ÷ compression ratio, where a ratio of 2 means stored data is half the logical size.

Worked example

A 2 TB full backup, 6 full copies, 0.08 TB changed daily, 14 incremental days, and 2× compression require (2 × 6 + 0.08 × 14) ÷ 2 = 6.56 TB.

Assumptions and limits

This simple retention model stores each full and daily changed-data set once. It excludes metadata, deduplication, snapshots, filesystem overhead, and offsite replicas; it is not RAID capacity.

Inputs are bounded to finite values shown in the form. Displayed results are rounded for readability (probability percentages and proportion fractions to four, other measures to two decimal places); whole-count outputs remain exact. A changed field clears a prior result so an outdated estimate is not presented as current.

References and related tools

These are direct calculations over user-supplied values; no external empirical benchmark is assumed.

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