On 4 Nov 2018 15:02:31 GMT, Frank Slootweg
wrote:

"J. P. Gilliver (John)" wrote:
In message , Pamela
writes:
On 18:49 30 Oct 2018, Char Jackson wrote in
news
[]
Defragging doesn't reclaim space.

Wouldn't a defrag reclaim slack space hidden in cluster tips?
[]
AFAIK, a fragmented file fills all the clusters it uses except the last
one, just the same as an unfragmented one.

What - I think - Pamela is hinting at, is that defragmentation can
combine the used contents of several partially filled clusters into one
or more clusters, thereby potentially freeing up clusters and hence
"reclaim space".

When files are stored on disk, the only partial clusters are each file's
final cluster, so of course you can't combine those.

That would corrupt the files that were using those partially filled
clusters, so AFAIK, no defragger would attempt to do that. They move
things around so that, as much as possible, files are laid out in a
contiguous fashion, but they don't/can't free up any space.

Where I think the idea of freeing up space via defrag comes from is the
edge case where an application wants to write a file to disk, and it
demands that the file be contiguous on disk.** You have enough total
free space, but not enough contiguous free space, so the operation
fails. Some defraggers help in this case because as part of the
defragging operation they "pack everything to the left", which is
largely unnecessary and is mostly done so that the graphic output looks
more pretty. Still, such "packing" would have the effect of creating a
larger contiguous space from the many smaller spaces, but the total free
space would remain unchanged.

**I'm trying to think of an example. Perhaps a container of some kind,
such as an encrypted volume or something that holds a virtual disk? I'm
struggling to think of an example where a file actually needs to be laid
out contiguously. Even the Windows pagefile doesn't care where it lands
on disk.

Bottom line, if someone is trying to free up disk space, the defragger
is the wrong tool for the job.

--

Char Jackson