Disk Utility says it couldn't unmount the disk: find what is holding it and erase anyway
Erasing or partitioning fails because something is still using the drive. How to find the app holding it, unmount it properly, and when you need Recovery.
730 guides
Mac storage, explained.
What fills your disk, where it hides, and what is safe to remove. Every guide gives you a way to check it on your own Mac.
The disk wasn't ejected because one or more programs may be using it: how to find which
macOS refuses to eject a drive but will not say what is using it. One command names the program, and here is what to do about each common one.
The disk you attached was not readable by this computer: what not to click
macOS offers Initialize, Ignore or Eject. Initialize erases the drive. Why the Mac cannot read it, how to find out, and how to keep the data if it matters.
First Aid process has failed: what to do next, on the Mac's disk or an external one
When Disk Utility cannot repair a disk, the order of what you do next matters. Back up first, then retry from Recovery, then decide whether to erase.
Copying to your external drive is painfully slow: the six usual causes
A copy that should take a minute takes an hour. Check the port speed, the cable, the drive type and the files themselves, with the command that proves each.
Encrypt an external drive on a Mac in two clicks, and the one thing you must not lose
A lost USB drive or backup disk is readable by anyone unless it is encrypted. How to encrypt one from Finder or Disk Utility, and what happens without the password.
Turn a folder into one compressed, optionally encrypted, disk image on your Mac
A disk image bundles a folder into a single file you can compress, encrypt and archive. How to make one in Disk Utility or Terminal, and which format to pick.
Deleted something on your Mac by mistake? Six places it may still be
Most deleted files can be brought back from the Trash, app bins, iCloud, Time Machine or snapshots. Where to look, in order, and when it is too late.
What changed on your Mac today? Find recently added and modified files in seconds
When space disappears or a file goes missing, the question is what changed recently. Finder, Spotlight and Terminal can each answer it, sorted by size.
Wiping an external drive on a Mac before you sell it, give it away or recycle it
Erasing a drive in Disk Utility does not always make the old files unrecoverable. What works for hard drives, what works for SSDs, and how long each takes.
Split one external drive into two on a Mac: partitions or APFS volumes
Partitions give each part a fixed size and its own format. APFS volumes share space. Which to use, how to set up each in Disk Utility, and what erases data.
Back up your Mac to an external drive with Time Machine, set up once and forgotten
A step by step Time Machine setup: which drive, how big, encryption, the first backup, what to exclude, and how to check it is actually working.