Manatee

"The item can't be copied because it's too large for the volume's format"

· 6 min read

This message appears when you drag a file of 4 GB or more onto a drive formatted as FAT32, which the Mac labels MS-DOS (FAT32). That format cannot hold any single file that large, however much free space the drive has. There are three ways out: reformat the drive as exFAT, make the file smaller than 4 GB, or split it into pieces for the trip.

Nothing is wrong with the file or the drive. The limit is built into the format itself, which dates from a time when a 4 GB file was hard to imagine.

Confirm the drive is FAT32

Select the drive in the Finder sidebar or on the desktop and press Command-I. In the Get Info window, look at Format under General. If it reads MS-DOS (FAT32), or MS-DOS (FAT), that is the cause.

Then check the file. Select it and press Command-I again; Get Info lists the size in bytes as well as gigabytes. The FAT32 ceiling is one byte short of 4 GiB, which is 4,294,967,295 bytes. A file at or above that figure is refused, even if the drive is otherwise empty.

Why so many drives are FAT32 in the first place: USB sticks and SD cards up to 32 GB are commonly sold formatted that way, because nearly every device can read it, including cameras, car stereos, TVs, printers and older PCs. Larger SD cards usually arrive as exFAT. So the error tends to show up with the old stick from the drawer, not the new external disk.

Option 1: reformat the drive as exFAT

exFAT was designed as the successor to FAT32. It has no file size limit you will run into, and current Macs and PCs both read and write it. This is the right fix when the drive is going to keep carrying large files.

Reformatting erases everything on the drive, so copy off anything you want to keep first.

  1. Open Disk Utility (Applications > Utilities).
  2. Choose View > Show All Devices, so the sidebar shows the physical drive and not only its volume.
  3. Select the drive itself, the top-level entry, and click Erase.
  4. Give it a name, choose ExFAT for Format, and GUID Partition Map for Scheme. If an older PC or another device does not recognize the drive afterward, erase it again with Master Boot Record as the scheme.
  5. Click Erase, wait for it to finish, then try the copy again.

One caution before you do this: the drive may be FAT32 because a device needs it to be. Some TVs, car stereos, older cameras and set-top boxes read only FAT32. If the stick’s job is to carry a video to one of those, reformatting will get the file onto the stick and then the TV will not see the stick. In that case the file has to get smaller instead.

If the drive will only ever be used with Macs, choose APFS or Mac OS Extended rather than exFAT. Both keep a journal that protects the file system if the drive is unplugged mid-write; exFAT does not.

Option 2: get the file under 4 GB

When the drive has to stay FAT32, or it is not yours to reformat, bring the file under the limit. For video, that means encoding it again at a lower bitrate.

A video that is only a little over 4 GB rarely needs much taken out of it. Long screen recordings, 4K phone video and camera files recorded at a high bitrate usually have plenty of headroom, and lowering the bitrate to fit under 4 GB often makes no difference you can see at normal viewing size. A screen recording that turned into a 4 GB file explains why recordings grow so large in the first place.

Manatee does this in its Shrink mode. Switch to Shrink, drop the video onto the window, and type a size in MB. For a FAT32 drive, 3900 leaves a comfortable margin under the ceiling. Manatee finds the quality that fits and writes a new file beside the original, which it never modifies. Copy the new file to the drive and keep the original on your Mac. How to shrink a video to a specific file size explains how bitrate, length and quality trade off.

Other large files are less forgiving. A disk image or a virtual machine cannot be squeezed much, and zipping video barely changes its size. For those, reformat or split.

Option 3: split the file for the journey

If the file only needs to ride on this drive and be put back together at the other end, split it. Terminal’s split command cuts a file into pieces of whatever size you choose:

split -b 3900m bigfile.mov bigfile.mov.part-

That produces bigfile.mov.part-aa, bigfile.mov.part-ab and so on, each under 4 GB. Copy the pieces to the drive. On the destination Mac, join them back together in order:

cat bigfile.mov.part-* > bigfile.mov

The pieces cannot be opened on their own; they exist only to carry the whole file. The rejoined copy is identical to the original byte for byte, and you can prove it by comparing checksums on both Macs, as shown in verifying a file arrived intact.

When the copy does not fail cleanly

Finder refuses the copy up front, which is the good outcome. Some other tools, and some cameras and recorders, do not. They write data until they reach 4 GB and then stop, leaving a file that looks roughly the right size but will not open, because the index a video needs was due to be written at the very end. If a large video arrived on a FAT32 drive that way, a file that copies to an external drive and arrives broken covers how to tell and what can be saved.

The same limit is also why many cameras hand you one long recording as several files. They close each file just before 4 GB and carry on seamlessly in the next. Why one recording arrives as several files shows how to join them on a Mac.

If the drive is not FAT32

A drive formatted as NTFS, which is common on disks set up on a PC, causes a different problem: macOS mounts it read-only, so you cannot copy anything onto it at all. Get Info shows the format as NTFS, and Sharing & Permissions says you can only read. Reformatting as exFAT is the fix there too, with the same warning about erasing the drive first.

Questions

Does the size of the drive matter? No. A large drive formatted as FAT32 has the same per-file limit as a 16 GB stick. Free space is not what the message is about.

Can I change FAT32 to exFAT without erasing the drive? Not with the tools built into macOS. Disk Utility erases the drive to change its format, so copy the contents off first and put them back afterward.

Will my TV read the drive once it is exFAT? Many recent TVs do and many older ones do not. The TV’s manual usually lists the USB formats it supports. If in doubt, leave the stick as FAT32 and shrink the video instead.