Will moving files to an external drive speed up my Mac?

It can, if the startup disk was nearly full: macOS needs free space for updates, caches and swap. Moving files off a disk with plenty of room makes no difference to speed.

Why can’t I copy a large file to my USB drive?

The drive is probably formatted as FAT32, which can’t hold files over 4 GB. Reformat it as exFAT in Disk Utility (erasing it), then copy again.

Can I use an external drive for Time Machine and storage at the same time?

You can add a separate APFS volume to the drive for files, but a drive that holds your only copy of files and your backups is a single point of failure.

Mac file guides

How to move files to an external drive on a Mac to free up space

By Vishva Variya · Updated November 7, 2026 · 4 min read

Short answer

Connect the drive, open it in Finder, then hold ⌘ while you drag files onto it. A plain drag between disks only copies, so nothing is freed; ⌘-drag moves. Use a drive formatted as APFS (Mac only) or exFAT (Mac and Windows), since FAT32 can’t hold files over 4 GB. Check a few files open from the drive.

Why didn’t dragging to my external drive free any space?

Dragging a file from your Mac to another disk copies it: the original stays where it was. To move it, hold ⌘ as you drag (the pointer loses its green plus sign), or copy it and then move the original to the Trash and empty the Trash. Space is only freed once the originals are gone.

How do I move files to an external drive?

1Connect the drive; it appears in Finder’s sidebar under Locations.
2Open the drive in one Finder window and the files in another.
3Hold ⌘ and drag the files onto the drive to move them.
4Open a few moved files from the drive to check they work.

Large Files are the best candidates: old video projects, disk images, archives and raw photos. See how to find large files and large videos.

Which format should the external drive use?

APFS: best for Macs on SSDs and flash drives. Not readable on Windows.
Mac OS Extended (Journaled): older Mac format, fine on spinning hard drives.
exFAT: works on Mac and Windows, with no 4 GB file limit. A good choice for a shared drive.
MS-DOS (FAT32): works almost everywhere but can’t store a file larger than 4 GB.

To change the format, use Disk Utility’s Erase, which wipes everything on the drive, so copy anything you need off it first.

What shouldn’t I move to an external drive?

Apps and anything in ~/Library: apps expect them on the startup disk.
Your Photos or Music library while the app is open. Move a library only with the app quit, then open it from the new place by holding ⌥ as the app starts.
Files you need every day, unless the drive is always connected.
Your only copy of something important: a single external drive is not a backup.

Moving big files off your Mac with Peekaboo

In Peekaboo’s Large Files, Move to Drive moves the files you pick to an external drive in one step, into a folder named for where they came from, so nothing overwrites anything on the drive. Nothing is deleted, files in use and iCloud placeholders are skipped, and it never uses the startup disk, a Time Machine drive or a network share. Undo moves them back, and waits if the drive is unplugged. It’s one of the cleanups in Peekaboo’s storage cleaner.

1Open Large Files and select the files to move.⇧⌘L
2Choose Move to Drive and pick the external drive.
3Need them back? Undo from Activity moves them home.⇧⌘Y

Questions

Will moving files to an external drive speed up my Mac?: It can, if the startup disk was nearly full: macOS needs free space for updates, caches and swap. Moving files off a disk with plenty of room makes no difference to speed.
Why can’t I copy a large file to my USB drive?: The drive is probably formatted as FAT32, which can’t hold files over 4 GB. Reformat it as exFAT in Disk Utility (erasing it), then copy again.
Can I use an external drive for Time Machine and storage at the same time?: You can add a separate APFS volume to the drive for files, but a drive that holds your only copy of files and your backups is a single point of failure.