In article ,
"John Gilmer" wrote:
snip-valiantly refraining from comment

- support for running a defragmenter while the volume is mounted.
(Don't ask.)

Well, I understand was the defragmenter does in a FAT system but since I
still don't understand how files are stored I can't
understand how that are
either fragmented or defragmented.

Consider a file system that writes empty blocks in numerical sequential
order. Now think of a file that's deleted. This leaves an empty
"hole" in the filled blocks. Now make a file whose size is less
than the "hole". Now you have a smaller hole that will be filled
with the next file that is written. That file is larger than the
hole so the hole gets filled, then the next block that isn't filled
is found and written into. Over time, all files, when viewed from
the geometry of the physical disk look like swiss cheese.

A defragmenter takes the whole file system and rewrites each file
such that all its block numbers are monotonically increasing.

Now, where this gets really, really ****ed up is when the defragger
program "forgets" which should be the next block (real easy to do
with off-by-one bugs) or has to call its error handling when it
can't do a fit or the block chain pointers become broken. The
last one is a feature of all Misoft OSes because of memory
management problems--but that's another nightmare in the not-an-OS
biz.


snip

/BAH

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