Re: [Bug-ddrescue] Bug-ddrescue Digest, Vol 102, Issue 1

[Scott Dwyer]

On 7/6/2014 3:02 PM, William wrote:
> These new features will help to insert DDrescue in professional and 
> forensics environments (mainly --no-reverse-pass). In such 
> circumstances, the program must to do exactly we ask it to do. 
> Automated behaviour is suitable for newbies.
Since everybody is so excited about the --no-reverse-pass option, I 
think I need to explain exactly what it does and does not do more clearly.

Ddrescue 1.18.1 does the copy phase in 3 passes. The first pass is 
forward with skipping, second pass is reverse with skipping, and third 
pass is forward with no skipping (everything is opposite of that if 
starting out in reverse). Then the trimming and splitting phases are 
done in multiple passes (it goes by error sizes so there is no set 
number on how many passes, but splitting in 1.18.1 has lots of head 
movement).

The --no-reverse-pass option only makes the second copy pass go the same 
direction, so the head jumps back to beginning for the pass. The copy 
phase still makes 3 passes.

If you want the control, make the skip size 0 (--skip-size=0). As 
Antonio has already stated in another thread, this is how to make it do 
the copying phase in one pass.

After the copying phase, there will still be the trimming and splitting 
phases. My new options will make each of those only do one pass each 
(MUCH more important for head movement than no-reverse).

So even if you use skip-size=0 and my --trim-sequentially and 
--split-sequentially options, there will still be 3 total passes 
(copying, trimming, and splitting).

If you want to do everything all in one pass (total control), you need 
--skip-size=0 --cluster-size=1 which will read sector by sector from 
start to finish. These options already exist without my help.

Scott