[TriLUG] Disk space calculations in Linux
william at trilug.org
Fri Jan 25 10:47:58 EST 2008
Yes. you divined my meaning perfectly :)
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. :-)
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