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Finder “Error code 0” when copying large files to external drive


“The operation can’t be completed because an unexpected error occurred (error code 0).” If you received this message when copying files from your Mac to an external hard drive or USB flash drive, there is a simple explanation.

Most external hard drives and USB flash drives, unless they are specifically marketed as Mac products, are formatted with the FAT or FAT32 file system. This is a Windows file system that rose to prominence in the 1990s before NTFS took its place in Windows systems of the early 2000s. The reason removable media like flash drives, memory cards, etc. still use FAT is because of its cross-platform compatibility with Mac OS X, Linux, and Windows. NTFS drives, on the other hand, can only be read (but not written to) by non-Windows systems.

Unfortunately, as technology progresses and the horribly outdated FAT32 file system continues to be used, issues will arise more often. For example, copying large files to an external drive in Mac OS X might lead to the following Finder error: “The operation can’t be completed because an unexpected error occurred (error code 0).”

Before cursing your Mac, it’s important to note this is an issue with FAT32 that Linux and Windows users experience as well. The cause is FAT32’s 4GB limit on individual file sizes. So while your drive might be 160GB in total, no single file can be larger than 4GB with FAT32. Now that that’s out of the way, let’s look at how you can get around it.

If the large file(s) you’re trying to copy are archives or images (zip, rar, dmg) you can extract all of the smaller files inside into a folder and copy them that way. This means your single 6GB zip file is now 6GB worth of separate files & folders.

The best advice, however, is simply to reformat your external drive to Mac OS X’s native file system, HFS+. Here’s how you do it:

  1. Temporarily back up any existing files on the drive to another location. Reformatting will erase everything on it.
  2. Open Disk Utility on your Mac and select your external drive on the list to the left.
  3. Choose the Erase tab and select Mac OS Extended (Journaled) from the Volume Format drop-down menu. Enter a name of your choice for the drive.
  4. Click the Erase button.

If you only use the drive on Macs, this is the perfect solution. You’ll be able to copy files of any size to it with HFS+ as the file system. If you still need to connect it to Windows machines, there are complications.

Windows does not read or write to HFS+ volumes unless software such as MacDrive is installed on the machine. This program is basically a driver for Windows that treats the Mac-formatted drive like any NTFS drive when it’s connected. The only other option would be to connect the HFS+ external drive to your Mac or your router and then share it over your local network to the Windows PC. Windows will be able to read and write to the HFS+ volume when accessed through the network as a share.

30 Comments Have Been Posted (Leave Your Response)

I just tried this suggestion and it worked beautifully – thanks!! Is there any reason why I can’t use the same procedure to re-format my flash drive back to FAT, so that it’s cross-platform compatibile again, now that I’ve moved the large files that I needed to?


You absolutely can format the drive back to FAT (called “MS-DOS” in Disk Utility) any time you’d like. It’ll work just fine after that.

thanks buddy. you helped me very much

Getting this error when trying to reformat:
Volume Erase failed with the error:

Could not unmount disk

please help!

As a producer, i’m always moving massive project files between home and studio, couldn’t figure it out until i found this, thanks alot, easy to follow and solved my problem instantly!

Thanks, worked like a charm. Trying to move some big files from my laptop over to my older desk top for storage, via the USB stick to transfer. Really worked well!

so every time i want to move large files between a windows pc at college and my mac i have to format my hardrive?

thank you very much! saved me :)

“Before cursing your Mac, it’s important to note this is an issue with FAT32 that Linux and Windows users experience as well.”

Works fine on my PC. Only my piece of crap mac gives me issues. What a pain in the ass.

So what are my options if I want to move files over 4GB from a Mac to PC that can’t be connected through a local network?

Travel-Ball Parent
October 21st, 2012, 9:14 AM

Dude, THANKS!!!!! Do you know how much of a headache you saved me from dealing with about 5 hours of video? Much appreicated! Someone needs to Yelp you and put 5 stars!

Thank you!! 1 minute fix saved me hours of work.

I need to reformat a hard drive to NTFS but I already have as an HFS+ and cannot undo with Lion 7
Thank you in advance

My USB 3 External drive (Seagate) is already formatted as “Mac OS Extended (Journaled) and still comes up with the Error 0. However, only when I want to copy from the hard drive to a folder into the external drive; if copy into the main directory in the external drive and then copy again into the folder everything works fine. Why does this happen?

I was having no trouble transferring videos of any length from my Final Cut Pro 10.0.7. I even copied an hour and a half movie to my 500 GB Western Digital “Passport” external hard drive. But when I upgraded to the Final Cut Pro 10.0.8, I suddenly can’t copy any videos to the external drive without getting that accursed error message. Why?

I got the same problem a few months before. I realized it was the drive fomrat (volume format) which caused issue while transferring large files. I had to set the volume format to “Mac OS Extended” instead of my earlier FAT32. It worked for me. More details here:

Thank you! I love you! Thank you! Worked perfect, phew!

Damn! I just spent money on one of these drives for the sole purpose of moving a big file from my iMac at home to a Windows computer at work. You would think they should tell you this on the packaging instead of wasting money.

if i do this, does it delete everything I had saved on my external hard drive prior to the format switch? I have a lot of information on it and pressing “erase” doesnt really ease my conscious…

i wish i could delete that comment…

Ikeep gettign this message when I try to trash
The operation can’t be completed because an unexpected error occurred (error code -8003).

Getting this error when trying to reformat:
Volume Erase failed with the error:
Could not unmount disk
please help!
This was a previous post but there was no response that I could find and I am having the same issue. Can someone please help? Thanks.

Actually there are a number of reasons why you should be annoyed with your mac. That error message is rubbish. Even on linux you’d get a more explicit error message. If you are moving a lot of files it doesn’t even tell you which file caused the problem. Don’t people consider that erm, shit

I know this is an old thread so this was likely not an option then, but there is now a format called exFAT that works with large file sizes and is compatible with both Mac and Windows.

WOW! Just followed your directions and it worked perfectly!
Thanks so much. A life saver.

Thank you so much for this great piece of advice, it worked perfectly and now I can copy movies of any size onto my hard drive to play off my PS3!

I love you man! You saved my life today :)

I just tried and got the Could not unmount disk error as well. Before this ive had NO problems with files on the thumbdrive. Any help would be appreciated.

So basically. exFat will show from Lion OSX on. If you have snow leopard, you are screwed and can only format it to MD DOS fat
The solution is to get the dmg full installation file (from purchases or from whatever other sources you have) and start the installation and get your osx updated to lion.
Once you are within 10.7.5 (which is the latest lion version), you are on the right track.

Solid; forgot about this, but o had to move some 4gb files that threw this error… will unzip