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Multiple-pass overwrite of EXT3 file on a journalled fs



Greetings all,

I am curious if anyone knows why utilities such as
'GNU shred' (part of coreutils) and 'wipe' say they
are not effective on journalled file systems-
especially EXT3.

Is it because you can't "guarantee" that the journal
has been flushed/wiped (i.e. you have the journal
'between' you and the actual data blocks on the
physical disk), or because of buffering, or some other
reason?

On the same note, does anyone know of any utility that
does overwrite EXT3?  Most specifically, I am Looking
for an open source utility that will do a
MULTIPLE-pass overwrite of any data blocks used by a
file.  (This is for a government related project and
DOD says it's not sufficient to just do a single
overwrite of all zero's).

Any help/pointers are greatly appreciated.  Thanks.

Below is an excerpt from the shred man page which
specifically mentions EXT3:

----
CAUTION: Note that shred relies on a very important
assumption: that the filesystem overwrites data in
place. This is the traditional way to do things, but
many modern filesystem designs do not satisfy this
assumption. The following are examples of filesystems
on which shred is not effective:

* log-structured or journaled filesystems, such as
those supplied with

    AIX and Solaris (and JFS, ReiserFS, XFS, Ext3,
etc.) 
----


		
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