Why Three Copies?
Three copies means your original data plus two backups. With two copies (original + one backup), a simultaneous failure of both — a fire, a power surge destroying equipment in the same room, or ransomware that encrypts both before you notice — loses everything. A third copy provides the buffer that makes simultaneous loss of all copies extremely unlikely.
Think of it as risk layers: one copy is zero redundancy; two copies protects against single hardware failure; three copies protects against correlated failures where the first backup and the original are lost together.
Why Two Different Media Types?
Different media fail for different reasons. Hard drives (spinning) fail from mechanical wear, head crashes, and motor failure. SSDs fail from NAND cell wear and controller failure. Optical media degrades chemically. Cloud storage is vulnerable to account compromise, provider outages, or accidental deletion. By storing copies on two different media types, you ensure that whatever failure mode takes out one copy cannot simultaneously take out the other.
Practical combinations: primary on NAS (hard drives) + backup on USB external drive (different physical drives); primary on laptop SSD + backup on NAS hard drives + cloud. The key is genuine media diversity, not just two hard drives in the same NAS.
Why One Copy Offsite?
An onsite disaster — fire, flood, burst pipe, theft — can destroy every device in your home simultaneously. An offsite copy means at least one copy survives even if your entire home is lost. Offsite does not have to mean a data center. A USB hard drive at a family member's house, rotated monthly, qualifies. Cloud backup (Backblaze, iDrive, Synology C2, Wasabi) is the lowest-friction offsite solution for most people.
For businesses and serious homelabbers, a second physical site (a VPS with enough storage, a colocation facility, or a family member's home with a NAS) provides the most robust offsite option.
Implementing 3-2-1 at Home
A practical home implementation: Copy 1 — original files on your laptop or desktop SSD. Copy 2 — local backup on a NAS (Time Machine for Mac, Windows Backup, or rsync for Linux). Copy 3 — cloud backup of critical files using Backblaze Personal Backup (~$9/month unlimited), iDrive (2TB from ~$70/year), or Synology C2 Backup (if you have a Synology NAS).
For a NAS-centric setup: Copy 1 — primary NAS (RAID for drive redundancy). Copy 2 — second NAS at a different location (a family member's house running Synology Hybrid Share or rsync). Copy 3 — cloud backup of irreplaceable data only (documents, photos) to Backblaze B2 or Wasabi at $6–7/TB/month.
3-2-1 Backup Implementation Options
| Copy | Role | Example Solutions | Cost |
|---|---|---|---|
| Copy 1 (primary) | Your working data | Laptop SSD, desktop drive, NAS primary | Already owned |
| Copy 2 (local backup) | Fast local recovery | NAS RAID, USB external drive, Time Machine | $80–300 (drives) |
| Copy 3 (offsite) | Disaster recovery | Backblaze Personal ($9/mo), iDrive, Synology C2, USB drive at relative's house | $0–120/year |
What Qualifies as a Different Media Type?
| Media Combination | Qualifies as 2 Different Types? | Notes |
|---|---|---|
| HDD + HDD | No | Same failure modes; same physical location makes it worse |
| HDD + SSD | Yes | Different failure modes; good combination |
| NAS HDD + Cloud | Yes (+ offsite) | Excellent; covers local and offsite in one step |
| Laptop SSD + NAS HDD | Yes | Good local 3-2-1 base; still need offsite |
| NAS + USB external at different address | Yes + offsite | Fully compliant 3-2-1; just remember to rotate |
Frequently Asked Questions
Does RAID count as a backup?
No. RAID protects against drive failure — one specific failure type. It does not protect against ransomware (the encryption spreads to all mirrors), accidental deletion (the deletion propagates instantly), or physical disaster (fire/flood destroys the whole NAS). RAID plus a backup is the correct approach, not RAID instead of a backup.
How often should I backup?
Depends on how much data you can afford to lose (your Recovery Point Objective, or RPO). For documents you work on daily, daily backup is appropriate. For a photo library that rarely changes, weekly is reasonable. For databases or code you work on continuously, continuous backup or version control (git) is appropriate. Most backup software supports scheduled automatic backups — set it and forget it.
What is the best cloud backup service for home users?
Backblaze Personal Backup is the most popular choice at ~$9/month for unlimited data from a single computer. For NAS backup, Backblaze B2 object storage at ~$6/TB/month is cost-effective with Synology Hyper Backup or Rclone. iDrive offers 2TB for ~$70/year and works on multiple devices. Synology C2 Backup is the easiest option if you have a Synology NAS — built-in integration with no extra software.
Is a 3-2-1 backup hard to set up at home?
The simplest implementation is: a NAS with automatic backup from your computer (Time Machine, Windows Backup, or rsync handles this automatically) plus Backblaze Personal Backup running in the background on your computer for cloud backup. Total setup time: 30–60 minutes. After that, backups run automatically on schedule with no manual intervention.