Re: Disk Defragmentation

On Monday 18 September 2006 18:46, ac wrote:
Mario Vukelic wrote:
On Sun, 2006-09-17 at 19:23 +0800, Joel Bryan Juliano wrote:
There is still some fragmentation on ext3 filesystems, on
most cases it's very minimal, but it also depends on time
or overall usage of ext3 filesystem before the
fragmentation is visible. In general fragmentation only
happens when you do many deletes and writes on a disk that
is nearly full.

In general fragmentation only happens when you do many
deletes and writes on a disk that is nearly full.

This is I understand, the important point.

If a disk is used as nearly full, it will not be able to
self-defrag as it would with more space. I understand that a
windows file is placed in the earliest space, and the disk
then fills in sequence, rather inflexible. Deletions and size
changes cause fragmentation immediately. I think that ext3
places a file in the body of the (empty space) partition, so
that a deletion will result in a (still large) empty space. A
bit simplistic but ok for my simplistic brain. --
ac

The important point to consider is that on a typical windows
system, the entire system is one partition. That includes every
file in every directory for all possible usage patterns. The
disk rapidly takes on the appearance of a pig's breakfast.
There's a minimally 750M swap file in there as well, scattered
over most of the disk.

Contrast that with conventional usage on *nix: swap is a
partition, so it has no effect on the rest of the
filesystem. /tmp is often a separate filesystem, or a tmpfs
which has no effect on the disk. /usr tends to be rather static
and files on it tend to remain in a contiguous group anyway,
which is the entire end purpose of defrag after all. The
various *bin and *lib directories tend to have files added
incrementally which then stay the same until significantly
large protions of them are changed at one time (upgrades).
Only /home would really benefit from defrag, but again the most
common usage is to incrementally add files which then stay put
(think large mp3 collections).

The reason Linux doesn't have a defrag isn't so much because
it's not needed, but more that it doesn't feature at all (much
like a plane doesn't need oars because it's not a boat).

alan

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