P
Paul
Ed said:
There are two aspects to defragmenters.
1) Actual defragmentation. To defragment a file, all a file needs is to be
contiguous. There is nothing to say it has to be placed at a particular
location on the disk. An example of a "pure" defragmenter, is Sysinternals
"contig" program. It just tries to put the file into a set of clusters
next to one another, and considers the job to be done at that point. If
you then used a "defrag map", there would be green dots all over the place
(no apparent order, but no fragmentation visible).
2) The second aspect, is "optimization". For example JKDefrag would move
big files to one area of the disk, folders somewhere else and so on. These
would be "optimization policies". The Windows built-in might "push everything
to the left" as its optimization policy. Optimization is a large part of
what distinguishes the various third-party defragmenters. That, and their
execution speed.
Some defragmenters even know how to move file system metadata, which is actually
a handy feature, because it makes it easier to "shrink" the file system later.
Apparently, Microsoft doesn't know how to do this (to the same extent),
while some defragmenter developers have figured it out.
The OS has a set of APIs for defragmentation. Most defragmentation products,
will be using these, because of their "safety" aspects. A side effect of "safety",
is relatively small sized disk commands are issued, as the defragmenter works.
On my disks here (cheapo disks), I get anywhere between 1MB/sec to 3MB/sec as
the defragmenter works. Frequently, it's better to use other techniques than
defragmentation, to clean up a file system. When a defragmenter isn't finished,
after an all-night run, that's when it's time to use something other than
a defragmenter to do the job.
The Windows 7 defragmenter, finishes in no time. And even if I haven't run it
in a while, it doesn't seem to take that long to finish. It's not at all like
my WinXP experience.
Paul
