[Sussex] Why Linux doesn't need defrag

[Steven Dobson]

Geoff

Nice to see you're still live - long time no see or hear.

On Thu, 2006-08-17 at 18:35 +0100, Geoff Teale wrote:
> To be honst I'm not convinced *any* file system needs defragging
> on a regular basis.

While I was forced to use Win2K in a previous job I would defrag the
NTFS disk in that laptop about every 3-6 months and I did notice a speed
improvement.  A friend that didn't did see a noticable reduction in his
laptop's performance until he ran the defrager on his laptop.  

> Whilst different filesystems storage structures will have an effect
>  I reckon the following factors are important:
> 
>  - the size of disks generally (the more free space you have, the
>  less time is spent looking for space to) - in fact ackowledging
>  that disk space is cheap  could be a driver to writing an I/O
>  system that sacrifices capactiy for a greater number of continguous
>  blocks on disk.
>  - I/O scheduling in the Linux kernel is pretty darn clever
>  - the speed of disks is so great now that the slow downs that
>  fragmentation may cause aren't noticed by j.random user.
> 
> .. I think the fact we're even discussing fragmentation in persitant
>  memory is testament to the fact that many of us once used a crap OS
>  on machines with very full 100MB hard disks.  :-)

Of this I complely agree.  The most heavly used filesystem I have is
still only using 21% of it's 62G size.  There is always plenty of free
area on that.

From the old days on a SunOS system I can remember those disks running
at >95% capacity and that system was slow - but then it was only a 68020
processor anyway and they never did run fast (compared to days'
systems).

However I feel that one of the biggest improvements in disk IO is the
amount of buffer space you now get onboard the disk itself.  When you
have enough memory in the device the device it self can reorgains the
sequence of writes so that the data is written efficiently to disk
minimising the head movements.

Steve

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