[TriLUG] Disk space calculations in Linux

[William Sutton]

Yes.  you divined my meaning perfectly :)


William Sutton


On Fri, 25 Jan 2008, Jeremy Portzer wrote:

> William Sutton wrote:
>> While we're discussing... how much space gets wasted in overhead of files
>> that allocate a particular block size but don't use all of the blocks?
>
> I think you mean, files that don't use all the bytes in a block.
>
> That is an important difference - du - disk usage - will list the actual
> disk usage.  The output of du will always be in increments of the file
> system block size (I'm not quite sure exactly how this is determined,
> but in most of my ext3 filesystems, this unit seems to be 4096 bytes,
> determined by running "dump2fs" - there may be simpler way to show this).
>
> For example, the following three files have these sizes shown by ls:
>
> $ ls -l dump*
> -rw-r--r--    1 root     root            0 Jan 24 20:40 dump0.txt
> -rw-r--r--    1 root     root            1 Jan 24 20:40 dump1.txt
> -rw-r--r--    1 root     root       120176 Jan 24 20:34 dump-hda6.txt
> -rw-r--r--    1 root     root        77492 Jan 24 20:34 dump-hdc1.txt
> -rw-r--r--    1 root     root        40910 Jan 24 20:33 dump.txt
>
> But du shows this:
>
> $ du -b dump*
> 0       dump0.txt
> 4096    dump1.txt
> 126976  dump-hda6.txt
> 81920   dump-hdc1.txt
> 40960   dump.txt
>
> Notice that a zero-byte file takes zero space on disk, but a 1-byte file
> takes 4096 bytes on disk, and all other files always use increments of 4096.
>
> For this reason, when you care about the actual space on disk, you
> should use "du" and not "ls".  This difference normally doesn't amount
> to much, but it can if you have lots of very small files.
>
> Not sure if this answers a question anyone asked.  :-)
>
> --Jeremy
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