I have run into this issue multiple times in Win10 (I don't think this issue is OS-specific, though) on both SSD and HDD partitions. They were all formatted to NTFS partitions and had compression enabled.

I had been moving a VMWare virtual machine (~320GB) across different partitions, which consisted of multiple 2GB and 10GB Virtual Disk segments. I always copied those files to an empty partition with ample space. On one occasion the partition had ~460GB of free space, and OS claimed "Disk full" midway through the copy process. On another occasion I had them copied to a partition with ~800GB of free space, and I saw the leftover space being ~140GB after the copy process. I had to manually run chkdsk /f on these partitions to reveal the actual amount of free space.

Many thanks in advance for the help!


This is most likely due to your use of compression. When you copy or move a compressed NTFS file to a different folder, NTFS decompresses the file, copies or moves the file to the new location, and then recompresses the file. This behavior occurs even when the file is copied or moved between folders on the same computer. Compressed files are also expanded before copying over the network. I would surmise the decompression of the virtual machine filled the partition.

  • Thanks for the reply. I double checked the files and saw NTFS compressed them from 320GB to 308GB. I doubt if they would actually inflate to ~2x of the original size during the copy. The last time I had the issue I copied the files from an EXT4 partition over LAN, and this still happened. – bloomfielderic Dec 11 '17 at 3:28
  • So disable compression on the files then transfer them – Ramhound Dec 11 '17 at 4:30

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