Re: [Bug-ddrescue] Reverse image

[Antonio Diaz Diaz]

Hello Reon,

Reon Toerien wrote:
> Is it possible to do a reverse image starting at the last block and jumping
> further back when bad blocks are encountered until block zero is reached? In
> other words everything works in reverse.

Currently not. When trimming backwards a block, ddrescue marks this 
block for later splitting as soon as the first bad sector is found.

Reading in reverse a sector at a time is very slow (less than 100kB/s. 
One month to read a 250GB disc). This is why ddrescue currently uses it 
only to trim bad blocks.


> If not could it be added as a feature request?

Of course. :-)


> Should help eliminate the read ahead cache on the drive where it reads 16MB
> ahead in a area that has bad sectors.

I guess it won't be simple. Does reading in reverse help if the drive is 
dumb enough that it always tries to read ahead forgetting previous failures?

What pass (copy, split, retry, all) would be more useful to run in reverse?

I am sure the wonderful people in this list will help find the most 
useful behaviour to implement in ddrescue 1.14. Thanks in advance for 
your feedback. :-)


Regards,
Antonio.