Re: Fragmentation vs free space

Tech-Archive recommends: Fix windows errors by optimizing your registry

On Fri, 22 Apr 2005 22:18:22 +0100, "Bobby" <bobby@xxxxxxxxxxxxxxxx>

>That has been my experience. Defragmenting a large drive with lots of room
>makes little difference.

This is true.

With FATxx, everything will be piled upat the "front" of the volume,
and the head travel will be minimal no matter how big it is.

With NTFS, core file system structures are stuck in the middle of the
volume, so the larger a near-empty volume, the more head travel there
will be - so it may pay to keep always-small-content NTFS volumes
small, even if there's no cluster size issues to consider.

>But defragementing an almost full, slow HD makes a big difference.

Yes, because the disk usage strategy is forced to change when the file
load hits the end of the volume.

Normally, new files are created in the large mass of free space at the
end of the volume, so they are usually unfragmented unless they are
held open and updated concurrently with other files.

Once the file load hits the end of the volume, the system is forced to
create new files within the gaps between existing files, and
fragmentation becomes a bigger problem. When you delete files to free
space, these create more gaps scattered across the volume, so you
still have the same problem until a defrag pulls it all back again.

The other reason to defrag is to purge deleted directory entries.

This is particularly usefulon FATxx volumes, because FATxx looks up
directory entries in a linear fashion, from start to end. A
slowly-growing directory bloated with lots of deleted entries will
itself be fragmented and slow to access

NTFS is more efficient in that directory access is indexed via some
sort of B-tree arrangement, so that a large number of directory
entries is better tolerated than it is in FATxx.



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