Ext3 users - Feb 2008 - Avoid Fragmentation of ext3

Hello,
i just want to know, how ext3 avoids fragmentation. Well, i think it works like
this (but i dont know...):
When the OS says to the filesystem, save the file, the file system looks, where
are free sectors laying together to use. when there is enough place the
filesystem try's to write the file without fragments. is there not enough
place, the fs wrote the file in the way, to create less fragemnts. some file
systems keep space after the file, for when the file grows. i dont know, works
ext3 in this way?
maybe somebody can explain it shortly.

thanks

frindly

On Thu, Feb 28, 2008 at 6:22 AM, Andre Nitschke
<andre.nitschke at versanet.de> wrote:
> Hello,
>  i just want to know, how ext3 avoids fragmentation. Well, i think it works
like
>  this (but i dont know...):
>  When the OS says to the filesystem, save the file, the file system looks,
where
>  are free sectors laying together to use. when there is enough place the
>  filesystem try's to write the file without fragments. is there not
enough
>  place, the fs wrote the file in the way, to create less fragemnts. some
file
>  systems keep space after the file, for when the file grows. i dont know,
works
>  ext3 in this way?
>  maybe somebody can explain it shortly.
Yes, that's the basic theory.  Various file systems execute it more or
less successfully.  I'd say ext3 is about average and XFS is quite
good at it.

There was a paper comparing file system fragmentation at OLS a few
years ago.  "The Effects of File System Fragmentation" by Ard
Biesheuvel, et. al.:

http://www.kernel.org/doc/ols/2006/ols2006v1-pages-193-208.pdf

-VAL