Secure delete with python

Andrew Dalke adalke at mindspring.com
Mon Sep 6 22:27:33 CEST 2004


Ville Vainio wrote:
> Seriously? What OSen are known for [writing new content at
 > another location of the disk]? I'd had thought that if
> the file size is unchanged, the data is always written over the old
> data...

It can even be filesystem specific.  Back in the days
of WORM drives (do people still use those?) you could write
once to a place on the drive, but read it many times.
(Write Once Read Many).  Changing a file meant writing a
new copy of it and writing a new index to point to the
new file, ignoring the old.  That is, all copies of the
file would stay on the disk.


The VMS systems always kept an old copy of the file around
unless you explicitly deleted it.  By default a directory
listing would only show the most recent copy of the file,
but you could tell it to show all the versions, which
would look like (roughly, been 15 years since I last saw VMS)
   MYFILE;1
   MYFILE;2
    ..
   MYFILE;94

It was believed this feature was a deliberate ploy of
DEC to sell more hard drives.  ;)


If you read a file then wait a while, and during that time
the OS decided to defragment the drive then the location
of the file could easily be changed from underneath you.


				Andrew
				dalke at dalkescientific.com



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