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From:	"Bill C. Riemers" <cygwin AT docbill DOT net>
To:	<cygwin AT cygwin DOT com>
References:	<16072 DOT 6666 DOT 10124 DOT 338022 AT gargle DOT gargle DOT HOWL> <00f301c31e12$c29efdb0$6400a8c0 AT FoxtrotTech0001> <00be01c31e15$944d0d50$78d96f83 AT pomello> <005601c31e26$77671260$6400a8c0 AT FoxtrotTech0001> <20030519175913 DOT GA24066 AT redhat DOT com>
Subject:	Re: SPARSE files considered harmful - please revert
Date:	Mon, 19 May 2003 19:27:06 -0400
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> I think you need to read the documentation a little more closely.  Either
that
> or provide references to the parts of the documentation that says that
normal
> RW operations would fragment a sparse file.

It is rather obvious.  Let say you have three blocks worth of data, and
is written into a file with a physical block followed by a sparse
block followed by a physical block.  No disk space is reserved for the
sparse block.  Why should it be, as it would defeat the whole purpose of
using sparse files?  So physically on disk you have two consecutive physical
blocks.  What then happens if you open the file in RW mode, seek to the
sparse
block and write some data?  You now have a file with three physics blocks.
However, unless the operating system is going to rewrite the whole file to
disk
again, the new block can not be written in consecutive order.  It is either
written
after the last block of the file, or somewhere else on disk.

Before:
   ... [BLOCK 1][BLOCK 3] ...

After:
   ... [BLOCK 1][BLOCK 3] ... [BLOCK 2] ...

Of course, if you run the defragmenter regularly, you can fix these
fragmented files.  But if it is a file you regularly modify, it is best not
to make
it a sparse file to begin with.


                                                  Bill




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