On Tue, Oct 02, 2007 at 01:47:48PM +0200, Ingo Freund wrote:
> On 02.10.2007 12:49, Paul Bijnens wrote (please find the answer below the 
> original text):
> > On 2007-10-02 12:34, Ingo Freund wrote:
> >> Hi list,
> >>
...
> > 
> >> - the wiki says the vtape-partitions should not
> >>   be in a amanda backup-to-tape setup - why?
> > 
> > Because you would make a backup of the backup that was being
> > written, possibly filling an infinite amount of diskspace.
> > Or what do you expect?
> > Note that the word "partition" is not really correct here.
> > Only the "subtree" needs to be eliminated.
> > 
> 
> I don't expect amanda filling infinite diskspace, why should it
> do so?

In the old days you could do a silly command like taking some existing
file and cat'ting it on to the end of itself.

   cat foobar >> foobar

There would be two independent pointers into the file, one for reading
from the file (at the start of the file) and one for writing to the
file (at the end of the file).  As both were moving through the file
at the same rate, the read pointer would never reach the end of the
file.  Thus the file would grow to take up the entire disk.  Current
versions of cat have a specific check for this condition.[1]

The same type of situation `could' occur if you try to back up a
directory tree and save the results in the same directory tree.
As the tree continually grew at the same rate it was being read,
the backup might not finish, but run out of storage space.

[1] a malicious user might see a way around this check using 2 cat's.
-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
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