difference between disk first aid using disk utility, safe start and macOS Recovery procedure

Hello, Gary Scotland.

Disk Utility > First Aid is the same in all cases.

After a normal boot or safe boot, First Aid cannot access the startup volume to make repairs.

But when used in recovery mode First Aid can unmount the Mac's startup disk and volume to run diagnostics and repairs.

Also, Disk Utility can now erase and partition an internal startup drive when booted in recovery mode (but not safe booted).

That's about it in the proverbial nut shell.

Be aware that running Disk Utility's First Aid on your boot volume from the Safe Mode or normal boot will not do any repairs. It only verifies the drive.

To be able to make repairs you must be booted into another volume, i.e. the Recovery Volume, so that the volume you want to repair can be unmounted. It can't unmount if it's the boot volume.

You're welcome. 🙂