Backing up a Mac to an external drive splits into two problems that people usually confuse: recovering a file you changed by mistake, and recovering a machine that no longer starts at all. Time Machine answers the first. A clone answers the second. Doing both costs you one extra drive and covers both.
Option 1: Time Machine
- Connect an external drive formatted as APFS or HFS+.
- Open System Settings → General → Time Machine.
- Click Add Backup Disk and choose the drive.
- Leave “Back Up Automatically” on.
The first run copies everything and takes hours. After that, only changes are copied, so backups are minutes. Snapshots are kept hourly for a day, daily for a month, and weekly for as long as the disk has room — which means you can go back to a version of a file from weeks ago, not just the last copy.
Two limits worth planning around. Time Machine will fill its disk and then start deleting the oldest snapshots, so a small drive means a short history. And while the backup disk is disconnected, Time Machine keeps local snapshots on the startup disk — useful for quick restores, but they disappear when the disk runs out of space.
Option 2: A Bootable Clone
A clone is an exact, sector-by-sector copy of your startup disk that you can boot from directly. Plug it into any Mac and you are working in seconds, without a restore step.
SuperDuper! makes this straightforward: select the source and destination, run the job, and the result is a bootable copy. It also does incremental updates, so the second run only changes what differs.
The clone’s weakness is the opposite of Time Machine’s. There is no history — the destination is a snapshot of one moment. Overwrite it with a bad clone and the previous state is gone, which is why a clone belongs next to a Time Machine disk rather than in place of one.
Choosing a Drive
A backup drive is a liability you buy, so pick conservatively. An SSD is faster and silent; a large spinning drive costs less per terabyte and is fine as a second copy. Whatever you choose, format it as APFS — macOS handles that natively, and Time Machine encrypted volumes on APFS are the simplest setup.
Before the first backup, it is worth knowing what is actually on the disk. DaisyDisk shows a folder tree by size, which usually reveals that caches, old iOS backups and archived downloads are a large share of what you are about to copy. Our guide to finding large files on Mac covers the same ground from the Finder side.
The Three-Copy Rule
One copy on your Mac, one on a local backup drive, one somewhere else. The third is the one that survives a fire or a theft, and it is usually the one people skip. If you only do two, make the off-machine copy the one that moves off-site — a local-only backup does not protect against the building.
For a comparison of tools beyond Time Machine, see our guide to the best Mac backup apps.
Frequently Asked Questions
Is Time Machine enough to restore a Mac from scratch?
Yes, if it has been running. Time Machine keeps hourly, daily and weekly snapshots and can restore the whole disk through macOS Recovery. The drawback is that restoring requires the recovery process, which is not the same as plugging in a drive and working immediately.
How often should I back up?
Time Machine handles this by running automatically once an hour while the backup disk is connected. If you use a cloning tool instead, before every significant change — updates, new apps, projects you cannot redo.
