Ralf Mardorf silver.bullet at
Sun Dec 3 08:31:31 UTC 2017

On Sun, 03 Dec 2017 09:19:59 +0100, Xen wrote:
>Ralf Mardorf schreef op 03-12-2017 8:36:
>> On Sun, 03 Dec 2017 08:25:41 +0100, Xen wrote:  
>>> dd  
>> Apart from myths about forensics, let's assume that overwriting data
>> one time is secure, but you still can't compare overwriting a whole
>> HDD using dd and shredding files on a partition of a HDD using the
>> shred command. There's something maintaining the available free HDD
>> space, e.g. to ensure a good performance. Again, we don't need to
>> defragment HDDs, it's an automated process were data is moved and
>> copied.  
>Actually this is incorrect.
>In 2009 there was work on a kernel patch that would allow a defrag 
>Apparently, it was never completed.
>Ext4fs does NOT automatically defragment files, unless I am mistaken 
>It intelligently pre-allocates files, but it does not defragment after 
>the fact.
>So there is no data being moved and copied (except by userspace 
>Of course user space programs can still leave temporary copies on disk.
>For which "sfill" is needed.

HDD's firmware might copy and move data, so a simple shred command,
even for a default mounted (not data) journaling ext file system remains
to be an issue, but indeed seemingly
is working around this issue, but software that "shred"s data usually
doesn't call sfill, too.

More information about the ubuntu-users mailing list