On 19/04/2017 14:32, Rob Morley wrote:
> On Wed, 19 Apr 2017 05:41:53 -0700 (PDT)
> jack4747@gmail.com wrote:
>
>> Il giorno domenica 9 aprile 2017 04:47:48 UTC+2, DisneyWizard the
>> Fantasmic! ha scritto:
>
>>> dd if=/dev/sdb of=/dev/sda &
>>>
>>
>> also the most stupid choice in this case.
>> dd will copy EVERYTHING, even empty space.
>
> The drive is nearly full, so there won't be much empty space.  If the
> drive is reading one file at a time it will likely have to perform seeks
> in a number of fragmented files (the likelihood of this is increased by
> the fullness of the drive) while dd will read each track consecutively.

Fragmentation of the files isn't the issue. If the smaller drive is
nearly full and/or contains lots of small files, using cp -a will be far
slower. For each file copied to the disc, the directory, allocation
structures and journal logs must be updated so it maintains a valid
filing system at all times. This will cause far more writing to the disc
than the simple one block written for each block read that dd performs.

---druck


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