Disk defragmenter in Linux

Tim ignored_mailbox at yahoo.com.au
Fri Dec 23 17:04:42 UTC 2005

On Fri, 2005-12-23 at 10:24 -0600, Mike McCarty wrote:
> Umm, I believe the argument is not that it defrags itself, just that
> the type of fragmentation it enjoys does not affect performance. Some
> sort of fertilizer[*], if you ask me.
> ...[snip]...
> The ext3 file system is so much superior to other file systems,
> that it runs as slowly as a fully fragmented disc ALL the time,
> even when everything is fully contiguous. It's equally slow.

I suppose there could be some truth in that.  If it was equally slow,
you wouldn't notice the difference.  ;-)  And if you were comparing it
to an OS that was really really bad with fragmented drives...

Since hard drives act in a non-linear fashion (data scattered about the
drive, where the drive always has to seek around the hardware), unlike a
tape (where data access has to work in a sequential manner for physical
reasons), and modern hard drives are quite nippy, it may well be that
you don't notice a small bit of hunting around.

Looking around at various explanations, some reasons why you might not
*usually* notice fragmentation seem quite straight forward:

e.g. "The ext2 and ext3 file systems most often used on Linux systems
also attempt to keep fragmentation at a minimum. These file systems keep
all blocks in a file close together. How they do this is by
preallocating disk data blocks to regular files before they are actually
used. Because of this, when a file increases in size, several adjacent
blocks are already reserved, reducing file fragmentation. It is,
therefore, seldom necessary to analyze the amount of fragmentation on a
Linux system, never mind actually run a defragment command. An exception
exists for files that are constantly appended to as the reserved blocks
will only last so long."

Snipped from <http://www.itworld.com/Comp/3380/nls_unixfrag040929/>

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