I recently need to transfer large tar files to an external USB hard drive from one Red Hat ES 5 server to another (neither with network connectivity).

Originally I was trying to move ~90gig tar file from the server to the external drive. This transfer worked, but when it came time to unmount the drive I received an I/O error refusing the device disconnect and then it unmounted, but not cleanly. I tried to do ~20-30gig files and the same thing happened. After breaking things up to ~10-15gig tar balls things were transfered just fine.

I was hoping someone could provide some insight as to why I experienced problems with the larger tar files (other then my own in-experience). Any information would be great!

  • Are you sure you exited the mounted folder before attempting to unmount the drive? Also, what method did you use to copy the file(s)? is it possible that it was still operating in the background?
    – Chris Nava
    Feb 24, 2011 at 5:41
  • Hey Chris, yes I was not in the mounted folder of the device and I ran fuser -m /dev/device1, which returned no processes still running against that device. I was just using tar from the directory of files on the server and creating the actual tar ball on the usb hard drive. Feb 24, 2011 at 13:22
  • 3
    It is possible that the files are still being trasferred "in the background" when the cp command returns. When the cp command returns, run the sync command. If the sync command blocks (does not return) then data is still being written to the drive. The sync command will return when the 'dirty' data has been completely flushed to the disk. After sync returns, are you still unable to unmount?
    – JeffG
    Mar 2, 2011 at 22:19
  • Also try lsof +D /mntpoint
    – Steven
    Mar 3, 2011 at 15:43

1 Answer 1


Try using the "sync" command before unmounting the drive. It's possible that it hasn't finished copying everything.

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