Re: Real size vs. Allocated size...

[James Rich <james@xxxxxxxxxxx>]

On Mon, 24 Jan 2005, Steve Landess wrote:

> In your case, the "allocated" size is probably the _minimum_ amount of 
> storage than can be allocated for the IFS object...it is probably the 
> "cluster size" on the disk, or the minimum number of sectors that must be 
> allocated for an IFS object.
>
> This phenomenon can also be observed on any PC hard disk...open a text 
> editor, put a single character into a text document, and save it to 
> disk...then go back and see how much storage it occupies.
>
> As a test, I just used Notepad to create a text file named XXX.TXT, and put a 
> single 'A' into it.
> when I use DIR to view the files in the folder, it shows a size of 5. 
> However, when I use Explorer to view the properties of the file, it says that 
> 4096 bytes are allocated, so on my PC the cluster size is probably 4096 
> bytes.

I got curious and did basically the same thing on my linux box which uses 
the XFS filesystem from SGI.  I did this:

cat > onebyte
a<control-C>

which resulted in a lower case "a" being put into the file "onebyte".  I 
verified this by opening onebyte in ghex.  Looking at the file with ls 
gives interesting results:

james@stumpy:~> ls -l onebyte
-rw-r--r--  1 james users 1 Jan 24 13:44 onebyte

This shows a size of 1.  But adding the -s argument to ls gives:

james@stumpy:~> ls -ls onebyte
4 -rw-r--r--  1 james users 1 Jan 24 13:44 onebyte

which shows that the file occupies 4 1024-byte blocks.

XFS has a website at http://linux-xfs.sgi.com/projects/xfs/ if you want to 
know more about it.

I believe other filesystems (perhaps ReiserFS?) allocate space in such a 
way that many small files do not occupy unnecessary disk space.  Perhaps 
hosting your files on some other machine and exporting them via NFS is a 
good solution?  Disk would be a whole lot cheaper.

James Rich

It's not the software that's free; it's you.
        - billyskank on Groklaw