On Wed, 19 Apr 2017 19:59:06 +0100
druck  wrote:

> 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.
>
That too. Having thought about the whole process of copying
file-by-file, ignore the file  fragmentation thing as insignificant,
unless all the file system overhead is cached in RAM and only
occasionally written to disk.   :-)
(And directory fragmentation is probably a bigger factor anyway.)

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