[ILUG] Re: contents of ILUG Digest, Vol 16, Issue 43

[Bill Stackpole]

Tim,
While I don't consider myself an authority on the
subject, I'm going to take a stab at answering your
question regarding conversion from NTFS to FAT. Note
the reference to "FAT" and NOT specifically "FAT32".
The version number of FAT you are using should be
irrelevant to answering this question - the filesystem
structures in the different number versions
(12/16/32/etc) that limit your ability to translate
from NTFS are largely the same.

So, the short answer I came up with is "not directly."
While one can COPY the contents of a file across
filesystems (from an NTFS source partition to a
FAT-based destination partition), there are many good
reasons why converting from one f/sys to another is
not easily accomplished.

Here's a (short?) explanation as to how I reached this
conclusion (I have left out some elements in my
description - strictly for clarity):

If you compare the structures of the NTFS and FAT
f/sys, you'll find that NTFS includes a number of
elements specifically designed to provide data
security and authentication. For example, each file in
an NTFS f/sys has an entry in a structure called the
"Master File Table" - and each entry includes elements
(permission bits) similar in function to the
permission bits in a Unix File system. In addition to
the permission bits, there is information on who
created the file, to what organizational group they
belong, etc. 

If one uses a Windows-NT-based operating system (e.g.
NT, XP, 2k, etc), these permission bits limit the
places to which a user can navigate in the f/sys as
well as which files they can access, read, execute and
so on. 

Since no such information (e.g.
owner/group/permissions) are available in a FAT (File
Allocation Table) based f/sys, allowing the content of
an NTFS f/sys to be translated would strip off all the
security functionality provided by NTFS - leaving the
contents of potentially sensitive files vulnerable to
anyone with a set of tools they could use to translate
the filesystem. 

Further, the way the NTFS f/sys stores each of the
parts to a given file is through a series of
structures called "data streams" (the concept of which
doesn't lend itself to existence in a FAT-based
f/sys). A single file in an NTFS f/sys generally
contains the permission and ownership information in
one "stream", the data content in another "stream",
while even more "streams" can exist (or be created) to
contain further data or information. If a file in an
NTFS f/sys was to be simply copied to a FAT-based
f/sys, only the FIRST data "stream" is moved (the
remaining streams have no logical place to be stored
in a FAT-based system and as such, are lost.) You can
consider the first two streams to be similar in
function to the "inode" and "data-block" structures of
a Unix EXTn f/sys - where one of the streams contains
metadata about the file, and the next stream contains
the "data". 

If you accept the above as a reasonable representation
of how NTFS f/sys's store data, logic should dictate
that that while most files can be COPIED from an NTFS
partition to a FAT-based partition, any permissions
and other intentional structures designed to limit
access to the file contents are stripped from the file
and lost forever.  A FAT-based filesystem doesn't have
the same data-holding structures as that of an
NTFS-based system so attempting to translate from one
f/sys to another would provide some pretty serious
hurdles with respect to how one might effectively move
the data, and what structures would need to be created
in the FAT f/sys to hold the information "translated"
from the NTFS f/sys (permissions and alternate data
streams initially being the most difficult to manage.)

I would be willing to bet that if you asked an equal
number of Sys-admins, folks involved in f/sys or OS
development, and computer security personnel, most of
those folks would tell you that it wouldn't be a good
idea to translate to FAT from NTFS, should any tools
actually be available to do so.

BTW, If you get any alternative answers to your
question, I'd be interested to hear them (e.g. anyone
who knows of tools that would allow such a
translation.)

Hope this helps!
Bill.

billatrit at nospam.yahoo.com
<strip the "nospam." from the email address>


--===============1527697857==
Content-Type: message/rfc822
MIME-Version: 1.0

Content-Transfer-Encoding: 7bit
From: Timothy Murphy <tim at birdsnest.maths.tcd.ie>
Precedence: list
MIME-Version: 1.0
To: ilug at linux.ie
References: <4077085A.2010907 at eircom.net>
<200404092105.43256.cj at nologic.org>
	<200404092138.49234.weeboy at conorwynne.com>
In-Reply-To:
<200404092138.49234.weeboy at conorwynne.com>
Date: Fri, 9 Apr 2004 22:41:28 +0100
Reply-To: tim at birdsnest.maths.tcd.ie
Message-ID:
<200404092241.28347.tim at birdsnest.maths.tcd.ie>
Content-Type: text/plain;
  charset="iso-8859-1"
Subject: Re: [ILUG] Mounting XP Partition
Message: 1

On Friday 09 April 2004 21:38, Conor Wynne wrote:

> > The "ro" part means read-only. I don't know what
kernel you have, but
> > allowing write access to ntfs can be dangerous -
I'm not sure it even
> > works fully.
>
> Was for a long time, unsure if I would risk it. I
would use a small fat32
> partition for file swapping.

As a matter of interest, is there any way of
converting an NTFS file system 
to FAT32?

-- 
Timothy Murphy  
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin
2, Ireland


--===============1527697857==


__________________________________
Do you Yahoo!?
Yahoo! Tax Center - File online by April 15th
http://taxes.yahoo.com/filing.html