1

For all my NTFS partitions, Ubuntu always shows 1~2GB more free space than Windows. What's the cause of this? Will some of my files be overwritten just because Ubuntu thinks there is more free space than there actually is?

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    Can you show us what you're looking at? Preferably with df -h output from Ubuntu and probably a screenshot from the windows side. You can edit your answer. It's possible this is a known issue but it's usually a good idea of showing a discrepancy if you're going to ask about it. – Bratchley Apr 5 '14 at 21:54
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    It's also worth knowing the volume size in case this is an indication of NTFS-3G and Windows treating the NTFS reserved zone differently when showing available space. – Bratchley Apr 5 '14 at 22:12
  • Linux ntfs support will always be somewhat limited. I would probably ignore whatever Linux says about size and be happy I can read and write from the partition. – Graeme Apr 5 '14 at 22:22
4

They measure the sizes differently by default. Under Linux, you can specify the --si parameter (which uses powers of 1000 not 1024) with df and du to get numbers that match up with how Windows calculates the sizes.

Compare

$ df -h  
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       119G   29G   89G  25% /

versus

$ df --si
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       127G   31G   96G  25% /

And on a file level

$ du -sh justbrowsing_20140331_nightly.iso 
589M    justbrowsing_20140331_nightly.iso

versus

$ du --si justbrowsing_20140331_nightly.iso 
617M    justbrowsing_20140331_nightly.iso

Explained in-depth here

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Free space in filesystems is always just a guess. Different numbers may mean different representations or different results of guessing. I wouldn't be afraid of that.

  • Several gigs of space is a pretty big difference. I could see if we were talking about a few Megs, but gigs indicates something else is going on. – Bratchley Apr 5 '14 at 22:10
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    No, free space is measured precisely. It's more than “maximum sum of the sizes of files you can add”, because of the space used by metadata which depends on exactly what files are added where. But there is no guessing involved. – Gilles Apr 6 '14 at 22:31

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