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From: "Gary R. Van Sickle" <g DOT r DOT vansickle AT worldnet DOT att DOT net>
To: <cygwin AT cygwin DOT com>, "'Vladimir Dergachev'" <vdergachev AT rcgardis DOT com>
Subject: RE: NTFS fragmentation
Date: Wed, 2 Aug 2006 18:08:57 -0500
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[cc'ing you per your request]

> From:  Vladimir Dergachev
> Sent: Wednesday, August 02, 2006 5:33 PM
> Subject: NTFS fragmentation
> 
> 
> Hi all, 
> 
>        I have encountered a rather puzzling fragmentation 
> that occurs when writing files using Cygwin. 
> 
>        What happens is that if one creates a new file and 
> writes data to it (whether via a command line redirect or 
> with a Tcl script - have not tried C
> yet) the file ends up heavily fragmented. 
> 
>        In contrast, native Windows utilities do not exhibit 
> this issue.
> 
>        Someone suggested to me that Windows requires an 
> expected file length to be passed at the time of open, thus I 
> searched on Google and found "fsutil" program that allows to 
> reserve space on the filesystem.
> 
>        I attached a small Tcl script that, when run, creates 
> two 30 MB files - one using regular open/write pair (and 
> which is fragmented into about 300 pieces on my system) and 
> one using fsutil/open in append mode/seek 0 method.
> 
>       To see the problem defragment your system, run the test 
> script and then run analyze and ask to view report. You will 
> see a.dat at top of the list, while b.dat never appears in 
> the report. 
> 
>        Despite the workaround, it is still kinda hard for me 
> to believe that anyone has designed a filesystem that needs 
> to know what is the file size going to be - especially for a 
> single program writing on an almost empty disk. Perhaps there 
> is some sort of environment variable that I need to set ?
> 
>         Any suggestions and comments would be greatly 
> appreciated.        
> Please CC me - I am not on the list.
> 
>                            thank you very much
> 
>                                         Vladimir Dergachev

I'll try your test case when I get a chance, but my WAG is that you're
seeing the effects of Cygwin's creation of sparse files by default for any
file beyond a certain size.  I unfortunately do not recall what that size
is.  What happens as you change FILE_SIZE and/or BUFFER_SIZE in your script,
to maybe a small multiple of your cluster size?

-- 
Gary R. Van Sickle
 



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