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Keep three copies of important files in total: the files you use and two backups. The 3-2-1 rule makes that baseline more resilient: store the copies on two types of media, keep one copy off-site, and ensure at least one backup is offline or otherwise protected from ransomware. Test that you can restore files from your backups.
What is the 3-2-1 backup rule?
CISA defines the rule as three copies of your data, including the primary copy, stored on two different types of media, with one copy kept off-site. In other words, you need two backups in addition to the files you actively use—not three backups on top of those files. CISA’s Data Backup Options and HHS OCR’s cybersecurity guidance describe this core approach.
The rule is a practical baseline, not a guarantee against every kind of data loss. Different media and locations help reduce the chance that one incident—such as a drive failure or a problem at your home or workplace—destroys every copy.
How should you arrange the three copies?
| Copy | Example location or medium | What it contributes |
|---|---|---|
| Primary | Your computer, phone, or other device | The files you use day to day. |
| Backup 1 | A local external drive or other separate storage medium | A nearby copy that can help with recovery; disconnect a removable drive when it is not in use. |
| Backup 2 | A different medium or a copy stored outside the primary location, such as a vetted cloud service | More protection if the primary device or location is lost or damaged. |
These are examples, not a required product list. CISA and HHS OCR identify local disk, hosted cloud, and removable media among possible storage approaches. An external drive can serve as a local backup, but it does not count as off-site merely because it is a separate device: the off-site copy must be outside the home or business location holding the primary data.
#1 Best Overall
- Easily store and access 2TB to content on the go with the Seagate Portable Drive, a USB external hard drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Should one backup be offline?
Yes. Keep at least one backup offline or otherwise restrict ransomware from accessing or changing it. CISA warns that ransomware may search for accessible backups and delete or encrypt them. Its ransomware guidance recommends offline, encrypted backups and regular checks that they are available and intact.
For a removable external drive, disconnect it when the backup is complete and store it safely. A drive that stays connected may be reachable by ransomware affecting the computer. Some cloud services offer immutable storage, but that protection depends on correct configuration and may involve cost or compliance considerations; do not assume every cloud backup is immutable or inaccessible to an attacker.
Rank #2
- Easily store and access 5TB of content on the go with the Seagate portable drive, a USB external hard Drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
How often should you back up, and how long should you keep copies?
There is no single schedule or retention period that fits every personal user in the cited guidance. CISA’s consumer advice is to back up frequently. Choose an interval based on how much recent work you could afford to lose, and keep versions or older copies for as long as you may need to recover from an accidental deletion or other problem you discover later. NIST’s guidance for managed service providers ties offline protection and update intervals to recovery-point and recovery-time objectives.
- Recovery point: How much recent work can you afford to lose? If losing a day of changes would be costly, back up more often than once a day.
- Recovery time: How quickly do you need files back? A nearby backup may restore faster, while an off-site copy can provide resilience when local equipment or the location is unavailable.
- Retention: How far back might you need to restore? Keep versions long enough for the kinds of mistakes or losses you want to recover from.
How can you tell whether your backups will work?
A backup is useful only if its files can be recovered. Periodically check that the backup is present and intact, and test restoring a few files. For an offline drive, reconnect it for the backup or recovery check, then disconnect it again when finished. If a test fails, investigate the cause and make a usable replacement backup before relying on that copy.
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Best Value
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- 【What You Get】 - 1 x Portable Hard Drive, 1 x USB 3.0 Cable, 1 x User Manual, Gift-type shell packaging ,Three-year manufacturer's warranty and free technical support services.
Rank #4
- Easily store and access 4TB of content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Rank #3
- Easily store and access 1TB to content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop. Reformatting may be required for Mac
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Practical checklist
- Count the files you actively use as one copy, then create two backups.
- Use two types of media and keep one copy outside the location of your primary data.
- Encrypt backups and keep at least one copy offline or otherwise protected from ransomware access.
- Disconnect and safely store a removable drive when it is idle; do not treat it as off-site unless it is stored elsewhere.
- Set backup frequency and retention according to acceptable data loss and recovery needs.
- Check backup integrity and test file restoration regularly.
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