Defragmentation needed with FreeBSD ...

Lowell Gilbert freebsd-questions-local at be-well.ilk.org
Mon Oct 3 07:11:46 PDT 2005


Kiffin Gish <kiffin at gish.demon.nl> writes:

> On Sun, 2005-10-02 at 17:11 +0400, Andrew P. wrote:
> > On 10/2/05, Tamouh H. <hakmi at rogers.com> wrote:
> > >
> > > >
> > > > I was just wondering if like in Windows disk fragmentation
> > > > arises, and if so then how should one go about defragmenting it?
> > >
> > > There is no fragmentation in the BSD file systems, that is something related
> > > to Windows only. You might want to add the line:
> > >
> > > fsck_y_enable="YES"
> > >
> > > to your /etc/rc.conf  in the event fsck finds errors on your disks.
> > >
> > >
> > > _______________________________________________
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> > >
> > 
> > Of course there is fragmentation.
> > 
> > UFS, particularly its implementation in FreeBSD is
> > more intelligent than NTFS/FAT32. When there is
> > enough free space on the disk (typically more than
> > 15%, see tunefs(8) for details), I/O is automatically
> > optimized to minimize fragmentation.
> > 
> > When your win32 box is idle, but the hdd is scratching
> > it's very annoying, because you know that windows
> > is swapping something.
> > 
> > When your bsd box is idle, but the hdd is scratching
> > it's quite pleasant, 'cuz that's some hard-working
> > daemons make sure that you don't loose any data,
> > and always can enjoy the maximum performance.
> > _______________________________________________
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> 
> So if I understand you correctly, this means that the disk is
> defragmented automatically in the background during idle use, e.g. I do
> not have to do anything else to enable it because it is already enabled.
> 
> Correct?

Not really.  Rather than trying to keep an entire file contiguous, UFS
just keeps reasonably large blocks contiguous, and all of the blocks
in the same part of the disk ("cylinder group").  

The basics of this are all still the same as in the original research
paper; see /usr/share/doc/smm/05.fastfs/paper.ascii.gz.

Also bear in mind that the term "fragmentation" is used to mean
something different in the Microsoft world than it is with respect to
Unix filesystems.  I have commented on that before on this list;
please see the archives to avoid repeating old discussions.  For example,
http://lists.freebsd.org/pipermail/freebsd-questions/2005-July/094544.html


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