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I have a 64GB USB (3.0) drive that is "compatible" with Mac OS. I can copy files from/to the disk at will. However, I want to move a file that is about 6GB to the disk. To my surprise, an error message appears saying that the file is too large for the volume's format !!

Now I know I have 50GB left on the disk, so can someone tell me a way that can just force the file into the disk and ignore the warning message ?

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1  
Well, what is the volume's format? Should we guess? –  GEdgar Jan 6 '13 at 17:54
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I'd assume it's FAT32, limiting the file size to 4GB –  XAleXOwnZX Jan 6 '13 at 18:33

3 Answers 3

up vote 9 down vote accepted

In your case, the problem is the file system on the drive as opposed to how it is connected to your Mac.

The drive is most likely formatted as FAT32 system. This is a typical partitioning format that is supported by practically all computers (windows, linux and mac os). FAT32 limits file sizes to 4GB and device sizes to 2TB (or 16 TB for 4 KB sectors). For you to be able to store a file greater than 4GB in size, you'd need to reformat the drive to either ExFAT (file size is limited to 16EB, or 16 BILLION TB) or a MacOS partition format (called HFS plus, file size limited to 8EB, or 8 BILLION TB). I'd recommend the MacOS partition format for it's reliability, but only if you're working in a strictly Mac OS environment. HFS plus is NOT supported by Windows. If you need to transfer files between computers of various OSs, I'd recommend ExFAT.

Note: Changing partition formats WILL DELETE ALL DATA ON THE DRIVE, so make sure you back up all the data on the drive before you start.

  1. Back up all your files on the USB drive onto a secure location on your Mac.
  2. Open Disk Utility by searching it in spot light or opening it from /Applications/Utilities
  3. Select your desired drive on the left side.
  4. Go to the "Erase" tab.
  5. Choose your desired partition format from the drop down menu, and name your drive as you please.
  6. Click "erase"
  7. Restore the files back to the drive.
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This is exactly right. Most USB drives ship with FAT32 formatting simply because it's universally supported across platforms, but it has technical limitations for file sizes. –  Ben Mordecai Jan 6 '13 at 18:36
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One correction, Fat32 limits the volume size to 2TB (or 16 TB for 4 KB sectors) –  maseth Jan 6 '13 at 18:51

If the USB stick is formatted as FAT32, the maximum file size is limited to 4,294,967,295 bytes (~4 GB). This limit is a consequence of the file length entry in the directory table and would also affect huge FAT32 partitions with a sufficient sector size.

If so, try to format USB thumb with exFAT it will increase the maximum file size to 16 EiB :)

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The only point to add to xalexownzx's answer regards the partition style.

For compatibility with Windows, all FAT32 partitions are MS-DOS style.

Use the Mac OS Extended (Journaled) format if you don't care about accessing the drive from a Windows machine.

If you might want to be able to boot a Mac sometime in the future with this drive without having to reformat it again you will need to format it with a GUID partition map. You can select this with the options button in Disk Utility.

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