Newbie Info

John Wendel john.wendel at metnet.navy.mil
Fri Oct 19 22:17:04 UTC 2007


aragonx at dcsnow.com wrote:
>> As you can gather from the other responses. defrag isn't used often on a
>> Linux system.  It isn't needed; the Linux kernel and friends do much
>> better job of allocating space on a hard disk.
>>
>> The following two sites begin the explanation.  You can explore more
>> from there.
>>
>> http://en.wikipedia.org/wiki/Defragmentation#_note-4
>> http://pl.atyp.us/wordpress/?p=241
> 
> I have had several threads on this very list about this subject.  The
> threads went something like this (dramatization):
> 
> Me:  I want to defrag my disk
> 
> Everyone else:  Shut up noob.  Linux doesn't need to do that winblows M$
> nonsense.
> 
> Me:  How could a filesystem never get fragmented.  It's not possible.
> 
> Everyone else:  Go back to M$ you.  We will have none of this Linux bashing.
> 
> Fast forward to today, a few years later.  I've got several file systems
> that are showing 20 - 30% non-contiguous as reported by fsck and I have no
> way other than a cp or dump to fix it.  This just doesn't seem right.
> 
> The real question is not so much if there is fragmentation or not.  It is,
> is there a performance difference or not.  Honestly, I can't say for sure.
>  I don't have reliable tests from years ago as to how long it took to
> copy, write or read from a file to compare it to.  I can say this, my
> performance is not bad enough to warrant the file system dump and restore.
> 
> So, in conclusion, after years of heavy usage, my file systems still
> perform reasonably well.  It would be nice to be able to defragment your
> hard drive but realistically, it isn't much needed.
> 
> I hope that answers your question with real world experience.
> 
> ---
> Will Y.
> 
> 

We haven't yet reached filesystem perfection!

A quick google for "ext4" reveals that the file system gods think that 
   it is worth the effort of writing a new (and incompatible with 
ext3) filesystem. The development version of the code is in the 
current kernel.org kernel (and in F8 ???). Among its features are a 
new block allocation scheme that keeps files contiguous and "online 
defragmentation" (whatever that is). I assume that in a few years 
we'll be complaining that the online defrag demon is taking too much 
CPU time on our 64 core box.

I amused that there is an entire industry devoted to selling software 
to defrag winblows filesystems.

Regards,

John





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