How to Back Up One Folder Automatically to an External Drive on a Mac

You keep a project folder, or years of photos, and you want a copy on an external drive every night, with last week's version still there the day something goes wrong. Time Machine is the obvious answer, but it is built to back up the whole Mac.

macOS has no setting that backs up a single folder on a schedule. Time Machine backs up everything except what you exclude, with one schedule and one retention rule for the whole Mac. For one folder, you can script rsync with launchd, or use an app that backs up folders: in Folia Files, you pick the folders, the drive, the schedule and how long backups are kept, and each backup is a dated copy you can open like any folder.

Can Time Machine back up only one folder?

Not directly. In System Settings › General › Time Machine, Options… has the two settings that matter here:

• Exclude from Backups: folders and disks Time Machine skips. To back up a single folder, you would have to add everything else to that list, and keep it up to date.
• Backup Frequency: Automatically Every Hour, Automatically Every Day, Automatically Every Week, or Manually. It applies to the whole backup.

The retention isn't yours to choose either: Time Machine keeps hourly backups for the past 24 hours, daily backups for the past month and weekly backups for all previous months, and deletes the oldest ones as space is needed.

That is what you want for the Mac as a whole, so keep it. A folder backup is a second layer next to it: another drive or a NAS, and a schedule of its own for the folders you can't afford to lose.

Option 1: rsync and launchd, if you like Terminal

macOS comes with rsync (on recent versions, it is openrsync). One command copies a folder to a drive and removes from the copy what you deleted:

rsync -a --delete ~/Projects/ "/Volumes/Backup SSD/Projects/"

To run it every night, you write a launch agent: a property list in ~/Library/LaunchAgents with the command and a StartCalendarInterval (hour and minute), loaded with launchctl. If the Mac is asleep at that time, launchd runs the job when it wakes up.

It works, and it is free. But you get one copy, not backups:

• No versions. The copy is overwritten every night: a file you damaged on Monday is damaged in the backup on Tuesday. The --link-dest option can make dated snapshots that share unchanged files, but then the naming, the cleanup of old snapshots and the checks are yours to write.
• An empty source empties the backup. If the folder ever comes up empty, because a drive didn't mount or a cloud folder isn't there, --delete faithfully deletes everything in the copy.
• Silent failures. If the drive isn't plugged in, nothing tells you the backup didn't happen. And macOS privacy protections can stop a background job from reading folders such as Desktop or Documents until you allow it in Privacy & Security.

Option 2: a sync, which isn't a backup

A sync keeps a second folder identical to the first: perfect for the same files on two Macs or on a NAS. But a mirror copies your mistakes too: a deleted file is deleted on the other side, a broken one replaces the good copy. Our guide on keeping two folders in sync explains when that is what you want. For a backup, you need older versions.

Option 3: scheduled folder backups in Folia Files

Set up the backup

1. Open the folder you want to back up in a pane, then choose Tools › Backups… (or click Tools in the toolbar, then Backups). The tool opens in a tab.
2. Click New Backup. It starts with the folder of the active pane under Folders to back up; add others with Add Folders… or by dragging them onto the card.
3. Under Destination disk, click Choose… and pick a folder on the external drive or on a NAS. Folder: is the name of the folder that will hold the backups there.
4. Under When, pick a Schedule:
   • At Regular Intervals: every 1 to 24 hours (every hour by default);
   • Every Day or Every week, at the time you choose;
   • Continuously, shortly after each change: a minute after the last change, and no later than ten minutes after the first one;
   • When the destination disk is connected: plug in the drive and the backup starts (at most once every ten minutes);
   • Manually.
5. Click Back Up Now for the first backup. Above the button, one sentence sums up what will happen, when and where.

Each backup is a dated folder, named like 2026-10-13 21-00-00, that holds your whole folder. Files that haven't changed since the previous backup are hard links to the copy already on the drive: as with Time Machine, a new backup only takes the space of what changed. Backups on the disk lists them: Open browses one in Folia Files, Restore… brings back a file or a folder.

Choose how long to keep backups

How long to keep backups works like Time Machine, except that you set the numbers:

• every backup of the last 24 hours;
• then one per day for 30 days (from 1 to 365);
• then one per week for 52 weeks, or with no limit;
• Delete the oldest ones when the disk is almost full (less than 5 % free by default).

The most recent backup is never deleted, and a full disk never causes the two most recent ones to be deleted. If even that doesn't leave enough room, the backup stops and says how much it needs to copy and how much space is free.

What happens when something goes wrong

• An empty folder never wipes your backups. If a folder you back up comes up empty while the previous backup had files from it, Folia Files makes no backup and deletes nothing, and tells you that a drive, a share or a cloud folder is probably missing. If you emptied it on purpose, remove it from the backed-up folders.
• Unreadable files aren't counted as deleted. A file or folder that couldn't be read this time stays in the new backup as the previous one had it. If even that fails, no old backup is deleted at that run.
• A missing drive only delays the backup. The tool says the destination disk isn't connected, and the backup runs when it comes back. A backup missed while the Mac was off or Folia Files was closed runs at the next launch.
• An interrupted backup resumes. Stop it, or unplug the drive: the next run reuses what was already copied, and an unfinished backup never passes for a complete one.
• Problems are reported. A backup that fails or ends with errors shows a banner, with Run Again and Show Backups.

Backups run while Folia Files is open, even with no window. To keep them going, turn on Open Folia Files at login, right under the schedule.

ExFAT drives and NAS shares

Dated backups rely on hard links. ExFAT and FAT drives, and most NAS shares, don't support them, and the destination card says so. There, Folia Files keeps one up-to-date copy, Current State, and at each backup sets aside the versions it replaces or deletes in Previous Versions, each kept for the whole period you chose. For complete dated backups, use an APFS or Mac OS Extended drive.

Restore a file or a folder

In the tool, Restore… next to a backup opens it: pick a file or a folder, then Restore to Original Location or Restore To…. If an item with the same name is already there and you choose to replace it, it goes to the Trash, and ⌘Z undoes the restore.

For a single file, the Versions module of the right sidebar is quicker (add it with the Modules button above the sidebar). Select the file in a pane: it lists the current version, the copies in your backups and the versions macOS keeps of documents, with Restore a Copy (next to the file, under a name of its own) and Replace with This Version…. In the website edition, it also shows the copies in Time Machine when its drive is connected (with Full Disk Access).

Which one to use

You want	Use
The whole Mac, restorable after a disaster	Time Machine
One copy of a folder, and you're at ease in Terminal	rsync with a launch agent
The same files on two Macs or a NAS, always identical	A sync
Folders backed up on a schedule, with dated versions to restore	Folia Files backups

Backups are in both editions of Folia Files. In the Mac App Store edition, you give Folia Files access to the folders and to the drive once (the Allow… button in the tool). The sync and backups page sums up both features.