file size on disk vs used drastically different

[Eric Shubert]

der.hans wrote:
> Am 15. Apr, 2010 schwätzte Shawn Badger so:
> 
>> I came across a weird problem this morning. What would cause a file to be
>> reported as 251M for used space and 1.3G for size on disk?
>>
>> [root at cc1lnx5 axprac]# ls -sh cafrap_1.dbf; ls -lh cafrap_1.dbf
>> *251M* cafrap_1.dbf
>> -rw-r----- 1 oraxprac axprac *1.3G* Apr 15 09:47 cafrap_1.dbf
>> [root at cc1lnx5 axprac]#
> 
> A bunch of nulls.
> 
> Essentially, the file has allocated 1.3GB of space, but since a bunch of
> what it's storing are nulls the filesystem cheats and doesn't use space
> for them.
> 
> That space can expand out during backups and other operations, so be
> careful copying it around.
> 
>> I have seen this to a smaller extent with some files but never a 
>> variance of
>> this size.
>> This file happens to be an Oracle 11G database table file.
> 
> I believe Oracle allots a configured amount of space for DB tables. The
> space alloted but not used should be nulls.
> 
> $ qemu-img create /tmp/Beispiel.img 10G
> Formatting '/tmp/Beispiel.img', fmt=raw size=10737418240
> 
> $ ls -sh /tmp/Beispiel.img ; ls -lh /tmp/Beispiel.img 0 /tmp/Beispiel.img
> -rw-r--r-- 1 lufthans lufthans 10G 2010-04-15 11:06 /tmp/Beispiel.img
> 
> It is to filesystem allocation what ticket overselling is to airlines :).
> 
> ciao,
> 
> der.hans
> 

Interesting.

I wonder if VMware thick virtual disks (vmdk files) exhibit this same 
kind of behavior. Anyone know?

Shawn, which type of filesystem is this using?

hans, which filesystem types (do you know of that) do this sort of 'cheat'?

-- 
-Eric 'shubes'