Help using "dd" command!

[Ricardo Ramos]

Hello, I'm making a paper about disk image aquisition software and I need a
little help from someone more experienced.

I used 2 programs to clone a disk on a GNU/Linux machine (Ubuntu), they are
"dd" and "DdRescue", and I used 3 different HDD, 120GB, 160GB and 500GB.

I captured the behaviour of the commands using the program pidstat, and the
reports showed that the programs had the same CPU usage patterns, but on
the other hand each HDD showed a different pattern.

[image: Imagem intercalada 1]
Percentage of CPU cores suing dd on the 120GB HDD.

[image: Imagem intercalada 2]
Percentage of CPU cores suing dd on the 160GB HDD.

[image: Imagem intercalada 3]
Percentage of CPU cores suing Ddrescue on the 120GB HDD.

[image: Imagem intercalada 4]
Percentage of CPU cores suing Ddrescue on the 120GB HDD.

Has you can see, it looks like it's a similar pattern, could anyone explain
to me one or both of the work so that I can find out why are they using
almost the same percentage of CPU cores and exactly the same cores.

Thank you.

PS: Sorry for the bad english, I'm a portuguese speaker.