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How to copy files to a USB drive on a Mac without errors

· 6 min read

Plug the drive in, find it in the Finder sidebar under Locations, and drag your files onto it. Because the drive is a separate disk, a normal drag copies rather than moves, so the originals stay on your Mac. When that does not work, the cause is almost always the drive’s format, and you can check which format it uses in a few seconds.

The basic copy

  1. Connect the drive. It appears in the Finder sidebar under Locations, and on the Desktop too if external disks are set to show there in Finder > Settings > General.
  2. Open a Finder window and click the drive to see what is on it.
  3. Drag files or folders from another window onto the drive’s window, or onto its name in the sidebar.
  4. Look for the green plus badge on the pointer before you let go. It means Finder will make a copy.
  5. Wait for the progress to finish before you do anything else with the drive.

If you want the files to leave the Mac rather than be duplicated, hold Command while dragging and the copy becomes a move. Copy, move, or alias when you drag a file on a Mac covers every modifier key.

When a file with the same name already exists on the drive, Finder asks whether to keep both, stop, or replace. Replace overwrites the version on the drive, so pause on that one.

When the drive will not accept anything

If the pointer shows no plus badge and the drop does nothing, or Finder says you do not have permission, check the format. Select the drive in the sidebar, press Command-I, and read the Format line in the Get Info window.

  • NTFS. Common on drives that were set up on a PC. macOS can read NTFS but cannot write to it on its own, so the drive behaves as read-only. Get Info shows “You can only read” under Sharing & Permissions.
  • MS-DOS (FAT32). Writable, but no single file can be 4 GB or larger. Copying a long video or a disk image fails with a message saying the item is too large for the volume’s format.
  • ExFAT. Writable by Macs and PCs alike, without the 4 GB file limit. This is usually the best choice for a drive that moves between computers.
  • APFS or Mac OS Extended. Native Mac formats, fully writable on a Mac. A PC will not read them without extra software.

Some SD cards and older USB sticks also have a physical lock switch on the side. If the format looks fine and the drive still refuses, check for one.

Reformatting a drive so it works

Reformatting erases everything on the drive. Copy anything you need off it first, and double-check which disk is selected before you click anything.

  1. Open Disk Utility, which lives in Applications > Utilities.
  2. Choose View > Show All Devices so you can select the whole drive, not just a volume on it.
  3. Select the drive at the top of its group and click Erase.
  4. Give it a name and choose a Format. For Scheme, GUID Partition Map suits most uses; Master Boot Record is the safer pick for older devices.
  5. Click Erase and wait for it to finish.

For a drive that goes between a Mac and a PC, choose ExFAT. For a drive only Macs will use, choose APFS. Choose MS-DOS (FAT) only for an older device, such as some car stereos and TVs, that reads nothing else, and accept the 4 GB limit that comes with it.

Hidden files that show up on other computers

On drives that are not in a Mac format, macOS keeps some extra information in hidden files: .DS_Store files for folder view settings, and files whose names start with ._ for extra details about each file. On a Mac you never see them. On a PC, a TV or a car stereo they sometimes appear as clutter, or as files that refuse to play.

They are harmless. You can delete them on the other device, and nothing on the Mac side depends on them.

Eject before you unplug

Always eject first. Click the eject button beside the drive in the Finder sidebar, or select the drive and press Command-E. Once it disappears from the sidebar, it is safe to pull out.

If you unplug without ejecting, macOS shows a notice that the disk was not ejected properly. Usually nothing is lost, but anything still being written at that moment may be incomplete. If ejecting fails because the disk is in use, quit the app that has a file open from the drive and try again.

Gathering files from several places before copying

Copies to a drive are rarely one tidy folder. It is a handful of documents from one place, a couple of exports from a project, a few photos you pulled out of the Photos library. Opening each location, finding the file and dragging it onto the drive one trip at a time is slow, and it is easy to forget one. How to gather files from different folders in one spot goes through the general problem.

Ledge lets you gather first. Drag each file or folder up to the notch at the top of a MacBook screen as you come across it, and it waits on a shelf until you are done collecting. Then open the drive in a Finder window, press Option-Space or click the notch to open the shelf, and drag the set onto the drive together. On a Mac without a notch, the shelf sits at the top center of the screen.

One thing to know before you rely on it: when Ledge hands items to Finder, it moves the file itself, so treat a drop from the shelf as a move. That is right when the files are leaving the Mac for good, such as a handover to someone else or an archive you no longer need locally. When you want a copy on the drive and the originals left where they are, use a normal Finder drag, which copies to a separate disk. If you move something by mistake, how to undo a file move you did by dragging explains the recovery.

Ledge works entirely on the Mac, with no account and no cloud step.

Questions

Why does my Mac say the USB drive is read-only?

It is almost always formatted as NTFS, which macOS can read but not write. Confirm with Command-I. To write to it, copy off anything you need and reformat it as ExFAT.

How do I copy a file larger than 4 GB to a USB drive?

The drive is formatted as FAT32, which cannot hold a file that size. Reformat it as ExFAT, which erases it, then copy again.

Does dragging to a USB drive delete the file from my Mac?

No. A drag to a different disk copies by default. Only a Command-drag moves the file.