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It is a known bug that Win 10 wrongly counts disk space.

Link1, Link2

In my case I want to copy 588GB from an external HDD partition to another internal SSD partition of size 605GB. The copy process of Total Commander stops after some hours and it is stated that the disk is full. Disk properties show an occupation of the partition of 605GB, i.e. completely full (there are no hidden files/folders or system files, no system partition, only data files). If I calculate the total size of the folders (marking them all and right click properties) the correct occupied size of 418GB is displayed. Treesize also shows the correct size.

The solutions concerning this bug that I found deal about how to display the correct occupied size. This I can do but I cannot copy all data because the disk is wrongly detected as full. Almost 200GB are vanished.

I use the Win Pro version 10.18363 including all updates on a new laptop with new SSD. For both partitions the compression is switched on. The cluster size is equal on both drives, 4kB. The SSD partition was newly created and no other data was there before.

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  • Do you know what bug this is? Not true here. Calculation of Disk Space is correct and reported the same by 3 different tools, one of which is Windows
    – anon
    Commented Feb 16, 2020 at 3:17
  • Perform a chkdsk /F <driveletter>: to ensure the file-system is not corrupt. BTW: Is it possible that at some time a very large numbers files were stored on the drive? In tat case the $MFT file may have grown to a large size occupying a lot space.
    – Robert
    Commented Feb 16, 2020 at 12:54

2 Answers 2

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In order of ease:

  1. If an image of the HDD is acceptable, use imaging tools such as Macrium Reflect.
  2. Create a live USB with another OS, e.g. Ubuntu and use it to copy the files. It's handy to have such a drive for emergencies, too, such as an unbootable SSD or HDD.
  3. Revert to a version of Windows that works.

That said, there is also the issue of file size on disk/SDD, which can be much greater than the size of the file itself. The cluster size, AKA allocation unit size, is, "the smallest amount of disk space that can be used to hold a file." For example, with a cluster size of 4 KB, a file of 100 bytes would take up 4 KB, and a file of 4,097 bytes (just one over the cluster size) would occupy 8 KB. Double check that the amount of data your trying to copy actually would fit on the SSD.

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The asker answers his own question.

Space is "emptied" after a restart of Windows or after chkdsk /f (as admin). Chkdsk gives the message that no errors were found. Also the issue is repeatable. So if I continue copying after a while the disk is full again. After a restart or chkdsk /f the space is freed. It is a shame that it required 4 interrupts to copy a 600GB partition to a never written SSD using an up to date Laptop and OS.

It would be interesting to know the reason for this behavior.

Screenhots after copying has stopped as disk is full (in this case the next file to be copied was larger than 111GB)

Screenshot before chkdsk /f or restart

Screenshot after chkdsk /f or restart

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