Scrub free disk blocks

Patrick O'Callaghan pocallaghan at
Sun Aug 29 00:42:55 UTC 2010

On Sat, 2010-08-28 at 15:12 -0700, JD wrote:
> On 08/28/2010 01:53 PM, Patrick O'Callaghan wrote:
> > On Sat, 2010-08-28 at 10:46 -0700, JD wrote:
> >> You need to study filesystem architecture to gain better
> >> understanding.
> > If you can't explain what you mean, just say so.
> >
> > poc
> >
> I can explain it alright - and I tried to tell you that a program
> can access all blocks of a file, direct and indirect, given that
> tha program has the access permissions for that file, but you ignored 
> it. Direct and Indirect blocks are only meaningful to the inode layer. 
> The file's offset will be computed and a block number arrived at. If 
> that block number is outside the range of the direct blocks, then the
> indirect blocks are accessed. Enough said.
> Explaining FS architecture is beyond the scope of this list, and
> certainly beyond this thread.

I've been using Unix since 1975 and am very well aware of how the
direct/indirect addressing scheme works. And I still fail to see what
this has to do with the scrub command. Are you saying that scrub
overwrites these blocks when deleting a file? If so, what is your basis
for saying so, given that the manpage explicitly states that "only the
data in the file (and optionally its name in the directory entry) is

OTOH if you're saying these blocks are irrelevant, you're contradicting
your original requirement of scrubbing any free space.


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