Is my data damaged after a “Disk Not Ejected Properly” warning?

Usually not. The warning means macOS couldn't guarantee buffered writes reached the disk. If nothing was actively writing, nothing was lost. Run First Aid in Disk Utility to repair directory damage early.

Why does my Mac keep ejecting drives at night?

Sleep. When the Mac sleeps it can cut power to the USB bus, the drive drops off, and macOS logs an improper eject. Eject before sleep — manually or automatically — or keep the Mac from sleeping with drives attached.

How do I find which app is using my external drive?

In Terminal, run: lsof +D /Volumes/YourDrive — it lists every process holding a file on the volume. Or use a utility like MountDock, which names the app directly and offers a safe force-eject.

“Disk Not Ejected Properly” on Mac: why it happens and how to stop it

MountDock Tips · 2026-07-15

If you use external drives or SD cards with a Mac, you’ve seen it: “Disk Not Ejected Properly”— eject the disk before disconnecting or turning it off. Sometimes you unplugged too fast. Sometimes the Mac was asleep and did it to itself. Either way, the warning is worth taking seriously — and it’s fixable.

What the warning actually means

macOS buffers writes to external volumes. When a disk disappears without a clean eject, the system can’t guarantee everything in that buffer reached the disk. Most of the time nothing was in flight and nothing is lost. But if a write was in progress — a photo import, a Time Machine snapshot, a Lightroom catalog update — you can get truncated files or a directory structure that needs repair. The risk isn’t the unplug itself; it’s the unplug during a write.

If you just got the warning

Plug the drive back in and let it mount.
Open Disk Utility → First Aid on the volume. It repairs directory damage before it compounds.
Check whatever was open or copying when it happened.
Eject properly this time — see below for the “in use” trap.

Why your Mac ejects drives while you’re not touching them

The overnight version of this warning — a pile of notifications waiting in the morning — is almost always sleep: the Mac cuts power to the USB bus, the drive drops off, and macOS logs it as an improper eject. Fixes, in order of effectiveness:

Eject drives before the Mac sleeps — or use a utility that does it automatically on sleep and remounts on wake.
System Settings → Energy → “Prevent automatic sleeping when the display is off” (heavy-handed; keeps the whole Mac awake).
Hubs and docks with their own power supply misbehave less here than bus-powered ones.

“The disk couldn’t be ejected because it’s in use” — the other half of the problem

The reason people yank drives is that macOS often refusesto eject — “because one or more programs may be using it” — without saying which program. The Terminal answer:

lsof +D /Volumes/YourDrive

That lists every process holding a file on the volume. Quit the guilty app and eject again. Common invisible culprits: Spotlight indexing (mds), QuickLook previews, antivirus scanners, and apps that keep recent-file handles open long after you closed the document.

The one-click version

This is the exact gap MountDock exists to fill: it lives in your Dock and menu bar, shows every external drive, card, and disk image, and when a volume is “in use” it names the app holding it and offers a safe force-eject. It can also eject everything before sleep and remount on wake — which ends the overnight-warning pile entirely. Free 14-day trial, $14.99 once, no subscription.