3-2-1 backup planner

The 3-2-1 rule keeps data safe: 3 copies, on 2 kinds of media, with 1 off-site. Enter what you're protecting and this plans the drives — including room for growth.

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Drives needed for 3-2-1
6 drives
2 per copy × 3 copies · 13.8 TB projected in 3 years
  • Primary copy (your live data)2 × 16 TB
  • Local backup (2nd media)2 × 16 TB
  • Off-site copy2 × 16 TB
Target size per copy
16.6 TB
Total raw capacity
96 TB

Why three copies. Your live data is copy one. A local backup on separate hardware is copy two, so a single drive or controller failure can't take both. An off-site copy is copy three — protection against theft, fire, or flood that a single location can't survive.

This planner sizes each copy independently and adds your free-space headroom so no copy ships full. RAID is not a backup: a mirrored array is still a single copy that can be wiped by ransomware, accidental deletion, or a failed rebuild — keep the second and third copies separate.