The 3-2-1 backup rule is the gold standard recommended by both NIST (SP 800-209, Storage Security) and CISA in their ransomware guidance. It ensures that no single event — ransomware, hardware failure, fire, theft, or flood — can permanently destroy your data.
What 3-2-1 Means
3 — Keep Three Copies of Your Data
Your original files plus two backups. If one copy is corrupted, encrypted by ransomware, or physically destroyed, two others remain intact.
2 — Store on Two Different Media Types
For example, an external hard drive AND cloud storage. Same-type media share vulnerabilities — a power surge or electrical fault can destroy two hard drives simultaneously. Different media types have different failure modes.
1 — Keep One Copy Offsite
If your home or office is flooded, burns down, or is burglarised, both your computer and your local backup drive are gone. Offsite means cloud storage, or a backup drive kept at a relative or friend’s home and rotated periodically.
A Practical 3-2-1 Setup for Home Users
Copy 1 — Original Files (Your Computer)
The files you work from every day. This is your primary copy.
Copy 2 — External Hard Drive (Local Backup)
Use Windows Backup, Time Machine on Mac, or free tools like Macrium Reflect. Schedule automatic backups — weekly at minimum, daily for important work. Critical: disconnect the drive after backup is complete. Ransomware encrypts permanently connected drives.
Copy 3 — Cloud Storage (Offsite Backup)
Backblaze Personal Backup ($9/month, unlimited storage) is the leading choice for whole-computer cloud backup. Alternatively, iCloud, OneDrive, or Google Drive work well for documents and photos. Ensure versioning is enabled — this lets you restore file versions from before a ransomware infection.
Ransomware encrypts files on every connected drive it can reach. A permanently connected external drive will be encrypted alongside your main files. Connect your backup drive only for scheduled backups, then disconnect it immediately.
Test Your Backups
A backup you have never tested is an assumption, not a backup. At least once per year, restore a few files from your backup to confirm the process works and the files are intact. Many people discover their backups were failing only when they need them.