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up vote 9 down vote favorite

Someone I know just made the following statement:

"I have 140.7 TB worth of files on my system"

Someone else said something along the lines of "how?" and the response was:

"Virtual RAM, Ubuntu has its quirks. /proc/core file"

I don't know much about Linux and wondered if someone could explain what the above is all about. I don't get how anyone could have 140.7 TB worth of anything, unless they have a very large number of hard disks.

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3  
What appears to be a file is not necessarily a file on the hard disk. And files' logical size isn't always the same as their physical size (i.e. storage required). – Daniel Beck♦ Oct 23 '11 at 21:02

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3 Answers

up vote 12 down vote accepted

You will get really strange numbers if you run disk usage utilities on virtual filesystems such as /proc or /sys and if they count "apparent" (sparse) size, not the actual disk usage.

For example, on my system, du -bhs /proc will report 128 TB, even though it occupies nothing – it is just a view into the kernel.

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up vote 4 down vote

No, that's not why. Sparse files appear a certain size because the file header lists it, but they contain far less data.

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5  
And amazing things happen when you try to back up sparse files with a backup program that doesn't understand them. Learned that on Xenix. – Fiasco Labs Oct 23 '11 at 21:49
up vote 1 down vote

One way could be that they have a large number of compressed files and are counting the size they would be when uncompressed.

Obviously this would depend on the type of file as some files compress further than others (e.g. text files) and others can't be compressed further (e.g. jpg, mp3) without losing data, but theoretically this could give the numbers your friend quotes.

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2  
Sure, if you had about 20TB of storage. – Ignacio Vazquez-Abrams Oct 23 '11 at 20:35
@IgnacioVazquez-Abrams - I'm not saying it's likely, just possible. – ChrisF Oct 23 '11 at 21:00
@IgnacioVazquez-Abrams: That's just ten 2TB disks. – grawity Oct 23 '11 at 21:16
2  
@grawity - full of text... – ysap Oct 23 '11 at 21:27
@ysap full of COMPRESSED text. – SplinterReality Oct 24 '11 at 5:39

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